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APOE gene variants in primary dyslipidemia

  • Yara Abou Khalil
    Affiliations
    Laboratory for Vascular Translational Science (LVTS), INSERM U1148, Centre Hospitalo-Universitaire Xavier Bichat, Paris, France

    Université de Paris, Paris, France

    Laboratory of Biochemistry and Molecular Therapeutics (LBTM), Faculty of Pharmacy, Pôle Technologie- Santé (PTS), Saint-Joseph University, Beirut, Lebanon
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  • Jean-Pierre Rabès
    Affiliations
    Laboratory for Vascular Translational Science (LVTS), INSERM U1148, Centre Hospitalo-Universitaire Xavier Bichat, Paris, France

    Laboratory of Biochemistry and Molecular Genetics, Centre Hospitalo-Universitaire Ambroise Paré, HUPIFO, AP-HP. Paris-Saclay, Boulogne-Billancourt, France

    UFR Simone Veil-Santé, UVSQ, Montigny-Le-Bretonneux, France
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  • Catherine Boileau
    Affiliations
    Laboratory for Vascular Translational Science (LVTS), INSERM U1148, Centre Hospitalo-Universitaire Xavier Bichat, Paris, France

    Université de Paris, Paris, France

    Genetics Department, AP-HP, CHU Xavier Bichat, Paris, France
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  • Mathilde Varret
    Correspondence
    Corresponding author. LVTS, INSERM U1148 CHU Xavier Bichat, Secteur Claude Bernard, 46 rue Henri Huchard 75018, Paris, France.
    Affiliations
    Laboratory for Vascular Translational Science (LVTS), INSERM U1148, Centre Hospitalo-Universitaire Xavier Bichat, Paris, France

    Université de Paris, Paris, France
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Open AccessPublished:May 21, 2021DOI:https://doi.org/10.1016/j.atherosclerosis.2021.05.007

      Highlights

      • FH refers to LDLR mutation carriers only while ADH includes all type IIa hyperlipoproteinemias (LDLR, APOB, APOE, PCSK9 …).
      • Rare APOE variants were reported in different dylipidemias including FD, FCH, lipoprotein glomerulopathy and bona fide ADH.
      • Due to the addition of non Mendelian factors, dyslipidemias associated with APOE variants often strongly overlap.
      • Screening of the APOE gene is warranted in the setting of ADH molecular diagnosis, along with LDLRAPOB, and PCSK9 genes.

      Abstract

      Apolipoprotein E (apoE) is a major apolipoprotein involved in lipoprotein metabolism. It is a polymorphic protein and different isoforms are associated with variations in lipid and lipoprotein levels and thus cardiovascular risk. The isoform apoE4 is associated with an increase in LDL-cholesterol levels and thus a higher cardiovascular risk compared to apoE3. Whereas, apoE2 is associated with a mild decrease in LDL-cholesterol levels. In the presence of other risk factors, apoE2 homozygotes could develop type III hyperlipoproteinemia (familial dysbetalipoproteinemia or FD), an atherogenic disorder characterized by an accumulation of remnants of triglyceride-rich lipoproteins. Several rare APOE gene variants were reported in different types of dyslipidemias including FD, familial combined hyperlipidemia (FCH), lipoprotein glomerulopathy and bona fide autosomal dominant hypercholesterolemia (ADH). ADH is characterized by elevated LDL-cholesterol levels leading to coronary heart disease, and due to molecular alterations in three main genes: LDLR, APOB and PCSK9. The identification of the APOE-p.Leu167del variant as the causative molecular element in two different ADH families, paved the way to considering APOE as a candidate gene for ADH. Due to non mendelian interacting factors, common genetic and environmental factors and perhaps epigenetics, clinical presentation of lipid disorders associated with APOE variants often strongly overlap. More studies are needed to determine the spectrum of APOE implication in each of the diseases, notably ADH, in order to improve clinical and genetic diagnosis, prognosis and patient management. The purpose of this review is to comment on these APOE variants and on the molecular and clinical overlaps between dyslipidemias.

      Graphical abstract

      Keywords

      1. Introduction

      ApoE is a major apolipoprotein that controls lipoprotein metabolism. ApoE is expressed in many cells, primarily in the liver, and also in the brain, spleen, kidneys, gonads, adrenals, and macrophages [
      • Marais A.D.
      Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease.
      ]. The widespread production of apoE indicates its importance in various pathways such as lipoprotein, fat-soluble vitamins and glucose/energy metabolisms, signal transduction, metastasis, angiogenesis or neurosciences.
      ApoE is a component of chylomicrons, very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), high-density lipoproteins (HDL), and lipoprotein (a) (Lp(a)). Classical knowledge is that LDL does not have apoE, nevertheless, since apoE binds to lipids through its C-terminal domain it seems difficult that it binds to HDL, VLDL, IDL and Lp(a) but not LDL at all. Indeed, lipoproteins isolated by flotation sequential ultracentrifugation showed that apoE represents 0.40%, 0.10% and 0.38% of the total mass of VLDL, LDL and HDL, respectively [
      • Bonaterra-Pastra A.
      • Fernández-de-Retana S.
      • Rivas-Urbina A.
      • Puig N.
      • Benítez S.
      • Pancorbo O.
      • et al.
      Comparison of plasma lipoprotein composition and function in cerebral Amyloid Angiopathy and Alzheimer's disease.
      ], and is found in HDL (61 ± 27%), VLDL (35 ± 25%), Lp(a) (4 ± 9%) and LDL (1 ± 1%) in fasting plasma [
      • Croyal M.
      • Blanchard V.
      • Ouguerram K.
      • Chétiveaux M.
      • Cabioch L.
      • Moyon T.
      • et al.
      VLDL (Very-Low-Density lipoprotein)-apo E (apolipoprotein E) may influence lp(a) (lipoprotein [a]) synthesis or assembly.
      ]. Lipoproteins isolated by anti-apoE immunoaffinity chromatography showed the presence of 21, 19, and 5 molecules of apoE in a portion of VLDL, HDL, and LDL respectively [
      • Sacks F.M.
      The crucial roles of apolipoproteins E and C-III in apoB lipoprotein metabolism in normolipidemia and hypertriglyceridemia.
      ]. ApoE plays a key role in regulating the clearance of these lipoproteins from the plasma and controls plasma lipid levels as well as homeostasis of tissue lipid content as the ligand for cell-surface lipoprotein receptors. ApoE mediates the interaction between apoE-carrying lipoproteins and the LDL receptor, the LDL receptor-related protein (LRP), the VLDL receptor, the apoE receptor-2 and heparan sulfate proteoglycans (HSPG) [
      • Huang Y.
      • Mahley R.W.
      • Apolipoprotein E.
      Structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases.
      ] (Fig. 1). As a ligand for heparin and HSPG in extracellular matrices or on cell membranes, apoE may also influence cellular responses to signals [
      • Marais A.D.
      Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease.
      ]. ApoE also contributes to the catabolism of VLDL particles. Once secreted, triglyceride-rich VLDL can be hydrolyzed by lipoprotein lipase (LPL). An excessive hepatic production of VLDL can cause a saturation of this pathway and an increase in plasma levels of triglyceride-rich lipoproteins [
      • Brouwers M.C.G.J.
      • van Greevenbroek M.M.J.
      • Stehouwer C.D.A.
      • de Graaf J.
      • Stalenhoef A.F.H.
      The genetics of familial combined hyperlipidaemia.
      ]. It is now well established that apoE, as an apo CIII co-factor, inhibits LPL and the triglyceride-rich lipoprotein lipolysis [
      • Packard C.J.
      • Shepherd J.
      Lipoprotein heterogeneity and apolipoprotein B metabolism.
      ,
      • Hara M.
      • Iso-O N.
      • Satoh H.
      • Noto H.
      • Togo M.
      • Ishibashi S.
      • et al.
      Differential effects of apolipoprotein E isoforms on lipolysis of very low-density lipoprotein triglycerides.
      ]. Also, apoE could increase the hepatic production of VLDL by activating the particle assembly cascade [
      • Mensenkamp A.R.
      • Jong M.C.
      • van Goor H.
      • van Luyn M.J.
      • Bloks V.
      • Havinga R.
      • et al.
      Apolipoprotein E participates in the regulation of very low density lipoprotein-triglyceride secretion by the liver.
      ]. These data underline the potential impact of a dysfunctional apoE on the metabolism of triglyceride-rich lipoproteins and the etiology of dyslipidemia. Furthermore, apoE plasma levels are associated with different causes of mortality: high apoE levels are associated with cardiovascular and cancer mortality while low apoE levels were causally associated with dementia-associated mortality [
      • Rasmussen K.L.
      • Tybjærg-Hansen A.
      • Nordestgaard B.G.
      • Frikke-Schmidt R.
      Plasma levels of apolipoprotein E, APOE genotype, and all-cause and cause-specific mortality in 105 949 individuals from a white general population cohort.
      ].
      Fig. 1
      Fig. 1Effect of APOE variants on the metabolic pathways of triglyceride rich lipoproteins.
      Several apoproteins including apoE are produced by the liver in the rough endoplasmic reticulum. ApoE, apoB100, apoC are then associated with triglycerides and cholesteryl esters to form VLDL particles. Nascent VLDL particles are secreted by the liver via golgi vesicles. Once in the circulation, VLDL particles can acquire more apoE and apoC molecules form HDL particles. In the vessels of peripheral tissues, VLDLs are hydrolyzed and converted to VLDL remnants by Lipoprotein lipase (LPL) located on capillary endothelium. ApoE, as a co-factor for apoCIII, inhibits LPL. VLDL particles are also converted to LDL by loss of triglycerides and apoE. ApoE binds with high affinity to cell-surface lipoprotein receptors including LDL receptor, the LDL receptor-related protein (LRP), the VLDL receptor, the apoE receptor-2. It also binds to cell surface HSPGs which facilitates the interaction with the LRP and possibly other receptors. Common and rare APOE variants are associated with dyslipidemia by affecting triglyceride rich lipoproteins metabolic pathways. Apo: apoprotein; VLDL: very low-density lipoprotein; HDL: high-density lipoprotein; LDL: low-density Lipoprotein; RER: rough endoplasmic reticulum; LPL: lipoprotein lipase; HL: hepatic lipase.
      The APOE gene is located at chromosome 19q13.2 and encodes a 317 amino acid apolipoprotein E precursor (NM_000041.4). After cleavage of the 18-amino acid signal peptide and glycosylation, mature apoE is secreted as a 299 amino acid protein with a relative molecular mass of 34 200 kDa.
      The variants that give rise to the apoE isoforms are rs429358, p.Cys130Arg (E4), and rs7412, p.Arg176Cys (E2). According to the frequencies given by the Genome Aggregation Database (gnomAd), with the sequencing of about 100 000 subjects from various disease-specific and population genetic studies, the rs429358 allele frequency is 14.25% and the rs7412 allele frequency is 6.542% in the total gnomAd population. Thus, the approximate prevalences for E2/2, E2/3, E2/4, E3/3, E3/4 and E4/4 are 0.4, 6.5, 0.9, 75.9, 14.3 and 2.0%, respectively. Which is overall in agreement with previous reports in healthy subjects [

      Mahley RW, Rall JSC. Chapter 119: Type III hyperlipoproteinemia (dysbetalipoproteinemia): the role of apolipoprotein E in normal and abnormal lipoprotein metabolism. In: Scriver R, Beaudet AL, Sly WS, et al, editors 2001;Metabolic and Molecular Base of Inherited Disease:New York: McGraw-Hil. https://doi.org/10.1036/ommbid.148.

      ,
      • Eichner J.E.
      • Dunn S.T.
      • Perveen G.
      • Thompson D.M.
      • Stewart K.E.
      • Stroehla B.C.
      Apolipoprotein E polymorphism and cardiovascular disease: a HuGE review.
      ,
      • Cenarro A.
      • Etxebarria A.
      • de Castro-Orós I.
      • Stef M.
      • Bea A.M.
      • Palacios L.
      • et al.
      The p.Leu167del Mutation in APOE Gene Causes Autosomal Dominant Hypercholesterolemia by Down-regulation of LDL Receptor Expression in Hepatocytes.
      ], but different from what is observed in hyperlipidaemic patients for whom the E4 isoform is more frequent and the E2 less frequent than in a control group [
      • Cenarro A.
      • Etxebarria A.
      • de Castro-Orós I.
      • Stef M.
      • Bea A.M.
      • Palacios L.
      • et al.
      The p.Leu167del Mutation in APOE Gene Causes Autosomal Dominant Hypercholesterolemia by Down-regulation of LDL Receptor Expression in Hepatocytes.
      ].
      ApoE accounts for 1%–8.3% of the total variance of LDL cholesterol [
      • Eichner J.E.
      • Dunn S.T.
      • Perveen G.
      • Thompson D.M.
      • Stewart K.E.
      • Stroehla B.C.
      Apolipoprotein E polymorphism and cardiovascular disease: a HuGE review.
      ]. Because the different isoforms have different affinity for lipoproteins and receptors, apoE2 and apoE4 have a significant impact on interindividual variation of lipid and lipoprotein levels in normal subjects. The residues that determine apoE isoforms are in the receptor-binding domain (154–168 and Arginine 190), separated from the lipid-binding domain (262–290) by a hinge region (218–233) (Fig. 2) [
      • Huang Y.
      • Mahley R.W.
      • Apolipoprotein E.
      Structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases.
      ,
      • Mahley R.W.
      • Weisgraber K.H.
      • Huang Y.
      • Apolipoprotein E.
      Structure determines function, from atherosclerosis to Alzheimer's disease to AIDS.
      ]. The structure and electric charge of apoE are crucial for the optimal function of the protein and the binding to lipids is necessary for receptor affinity. Once binding to lipoproteins, apoE undergoes conformational changes and adopt a circular horseshoe shape in which the lipid -binding and the N-terminal domains join to wrap around the lipoprotein and the critical residues for binding, 154–168 and Arg-190, meet nearby [
      • Mahley R.W.
      • Weisgraber K.H.
      • Huang Y.
      • Apolipoprotein E.
      Structure determines function, from atherosclerosis to Alzheimer's disease to AIDS.
      ]. In apoE4, the substitution Cys130Arg lead to a more compact structure, due to N- and C- terminal ends interaction, which changes its affinity preference from HDL to VLDL but have less impact on the receptor binding properties [
      • Mahley R.W.
      • Weisgraber K.H.
      • Huang Y.
      • Apolipoprotein E.
      Structure determines function, from atherosclerosis to Alzheimer's disease to AIDS.
      ]. ApoE4 is associated with higher apo B, total-, LDL-, and remnant-cholesterol levels [
      • Rasmussen K.L.
      • Tybjærg-Hansen A.
      • Nordestgaard B.G.
      • Frikke-Schmidt R.
      Data on plasma levels of apolipoprotein E, correlations with lipids and lipoproteins stratified by APOE genotype, and risk of ischemic heart disease.
      ] due to its preference for VLDL, and its higher production rate [
      • Blanchard V.
      • Ramin-Mangata S.
      • Billon-Crossouard S.
      • Aguesse A.
      • Durand M.
      • Chemello K.
      • et al.
      Kinetics of plasma apolipoprotein E isoforms by LC-MS/MS: a pilot study.
      ], and to its higher VLDL-lipolysis activity, or less inhibitory effect, relative to apoE3 [
      • Hara M.
      • Iso-O N.
      • Satoh H.
      • Noto H.
      • Togo M.
      • Ishibashi S.
      • et al.
      Differential effects of apolipoprotein E isoforms on lipolysis of very low-density lipoprotein triglycerides.
      ] (Fig. 1). The other classical hypothesis, according to which the increased level of LDL in apoE4 carriers would be due to the downregulation of LDL receptor expression consequent to the accelerated hepatic uptake of apoE4-rich VLDL, could complete the pathophysiology of the apoE4 isoform. The substitution Arg176Cys in apoE2 causes the disruption of a salt bridge, lowers the positive potential, and alters the receptor-binding domain which affects drastically apoE2 affinity for its receptors (<2%) but not its affinity for HSPG [
      • Huang Y.
      • Mahley R.W.
      • Apolipoprotein E.
      Structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases.
      ]. Thus, apoE2 is associated with higher remnant-cholesterol levels [
      • Rasmussen K.L.
      • Tybjærg-Hansen A.
      • Nordestgaard B.G.
      • Frikke-Schmidt R.
      Data on plasma levels of apolipoprotein E, correlations with lipids and lipoproteins stratified by APOE genotype, and risk of ischemic heart disease.
      ], as observed for 1–10% of the apoE2 homozygotes, under the influence of other genetic or environmental factors, who develop type III hyperlipoproteinemia (OMIM #617347). These factors (oestrogen deficiency, hypothyroidism, obesity and diabetes) lead to a saturated or impaired lipoprotein clearance. ApoE2 also inhibits the VLDL lipolysis significantly more than apoE3 and apoE4 [
      • Hara M.
      • Iso-O N.
      • Satoh H.
      • Noto H.
      • Togo M.
      • Ishibashi S.
      • et al.
      Differential effects of apolipoprotein E isoforms on lipolysis of very low-density lipoprotein triglycerides.
      ] probably by a reduction in the apoCII content of VLDL [
      • Huang Y.
      • Liu X.Q.
      • Rall S.C.
      • Mahley R.W.
      Apolipoprotein E2 reduces the low density lipoprotein level in transgenic mice by impairing lipoprotein lipase-mediated lipolysis of triglyceride-rich lipoproteins.
      ] (Fig. 1). Thus, explaining why apoE2 is also associated with lower apo B, total-, and LDL-cholesterol levels, relative to apoE3 [
      • Rasmussen K.L.
      • Tybjærg-Hansen A.
      • Nordestgaard B.G.
      • Frikke-Schmidt R.
      Data on plasma levels of apolipoprotein E, correlations with lipids and lipoproteins stratified by APOE genotype, and risk of ischemic heart disease.
      ]. The other classical hypothesis, according to which the decreased level of LDL in apoE2 carriers would be due to an opposite mechanism to that of apoE4 (the relative impoverishment of apoE2 in VLDL would slow down hepatic uptake and consequently upregulate the LDL receptor), could complete the pathophysiology of the apoE2 isoform.
      Fig. 2
      Fig. 2Distribution of the APOE gene variants in the apoE protein.
      On average, apoE2 lowers total cholesterol levels by approximately 14 mg/dL and apoE4 raises them by approximately 8 mg/dL [
      • Eichner J.E.
      • Dunn S.T.
      • Perveen G.
      • Thompson D.M.
      • Stewart K.E.
      • Stroehla B.C.
      Apolipoprotein E polymorphism and cardiovascular disease: a HuGE review.
      ]. Thus, although LDL contains only few apoE, its isoforms influence LDL concentration and size along with many other factors including sex, age and triglyceride levels. The recent analysis of 228 serum metabolites in a cohort of 2234 young Finns showed that the apoE4 isoform influences LDL and VLDL particle sizes as well as their composition increasing their concentrations of free/esterified cholesterol, triglycerides, phospholipids and total lipid, thus increasing their size [
      • Karjalainen J.-P.
      • Mononen N.
      • Hutri-Kähönen N.
      • Lehtimäki M.
      • Juonala M.
      • Ala-Korpela M.
      • et al.
      The effect of apolipoprotein E polymorphism on serum metabolome - a population-based 10-year follow-up study.
      ]. The opposite being observed for the apoE2 isoform [
      • Bach-Ngohou K.
      • Giraud F.
      • Krempf M.
      • Bard J.M.
      Influence of remnant accumulation markers on plasma concentrations of two lipoprotein(a) subspecies (containing or free of apoE).
      ]. Furthermore, apoE isoforms influence the Lp(a) mass that is 65% higher for apoE4 homozygous carriers relative to apoE2 homozygous carriers [
      • Moriarty P.M.
      • Varvel S.A.
      • Gordts P.L.S.M.
      • McConnell J.P.
      • Tsimikas S.
      Lipoprotein(a) mass levels increase significantly according to APOE genotype: an analysis of 431 239 patients.
      ].
      In addition to the three major isoforms apoE2, E3 and E4, three minor apoE isoforms have been observed by isoelectric focusing, E1, E5, and E7, each one presenting several nucleotide sequence variants with different amino acid substitutions [
      • Saito T.
      • Matsunaga A.
      • Fukunaga M.
      • Nagahama K.
      • Hara S.
      • Muso E.
      Apolipoprotein E-related glomerular disorders.
      ]. The minor E1 isoform has an isoelectric point more acid, by two units of charge, than apoE3 due to either p.Lys164Glu, p.Arg168Gly-E2, p.Gln174_Gly190del variants (Table 1). The apoE1 p.Lys164Glu variant, within the receptor binding domain of apoE, is produced at a higher rate and catabolized significantly slower than apoE3, due to its reduced affinity for the LDL receptor and for heparin [
      • Moriyama K.
      • Sasaki J.
      • Matsunaga A.
      • Arakawa F.
      • Takada Y.
      • Araki K.
      • et al.
      Apolipoprotein E1 Lys-146–--Glu with type III hyperlipoproteinemia.
      ,
      • Mann W.A.
      • Lohse P.
      • Gregg R.E.
      • Ronan R.
      • Hoeg J.M.
      • Zech L.A.
      • et al.
      Dominant expression of type III hyperlipoproteinemia. Pathophysiological insights derived from the structural and kinetic characteristics of ApoE-1 (Lys146-->Glu).
      ] (Fig. 1). The minor E5 isoform has an isoelectric point more basic by two units of charge than apoE3, due to either p.Glu21Lys, p.Gln99Lys, p.Pro102Arg, p.Val153_Arg160dup, or p.Glu230Lys variants (Table 1). The apoE5 p.Glu21Lys variant, within the N-terminal domain of apoE, presents a twofold increased receptor-binding activity while the activity is unaffected by the apoE5 p.Pro102Arg variant also localized in the N-terminal domain [
      • Wardell M.R.
      • Rall S.C.
      • Schaefer E.J.
      • Kane J.P.
      • Weisgraber K.H.
      Two apolipoprotein E5 variants illustrate the importance of the position of additional positive charge on receptor-binding activity.
      ] (Fig. 1, Fig. 2). This indicates that the enhanced receptor-binding activity of basic apoE isoforms depends on the position at which additional positively charged amino acids are incorporated. The apoE5 p.Glu230Lys variant, in the heparin binding domain, displays enhanced receptor- and heparin-binding activity, but decreased catabolism in cultured fibroblasts [
      • Feussner G.
      • Scharnagl H.
      • Scherbaum C.
      • Acar J.
      • Dobmeyer J.
      • Lohrmann J.
      • et al.
      Apolipoprotein E5 (Glu212-->Lys): increased binding to cell surface proteoglycans but decreased uptake and lysosomal degradation in cultured fibroblasts.
      ] (Fig. 1, Fig. 2). Since receptor-mediated endocytosis of apoE lipoproteins is facilitated by proteoglycan ligands transfer, the stronger binding of apoE5 p.Glu230Lys variant to proteoglycans could reduce the rate at which it is finally delivered to the endocytosis pathways. The minor E7 isoform, also named apoE-Suita, has an isoelectric point more basic by four units of charge than apoE3, due to the replacement of two glutamine residues by two lysine residues at positions 262 and 263 in the lipid-binding domain [
      • Maeda H.
      • Nakamura H.
      • Kobori S.
      • Okada M.
      • Mori H.
      • Niki H.
      • et al.
      Identification of human apolipoprotein E variant gene: apolipoprotein E7 (Glu244,245–--Lys244,245).
      ] (Fig. 2). Each of the two nucleotide variants contributing to the apoE7 isoform, rs140808909 and rs190853081, are only found in the Japanese population with a relative frequency of 0.7% for the apoE7 allele in a cohort of 1269 Japanese subjects [
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]. According to the frequencies given in the Genome Aggregation Database, with the sequencing of about 8000 Est Asian subjects from various disease-specific studies, the rs140808909 and rs190853081 frequency is 0.27% for both, giving a frequency of 0.073% for the apoE7 allele.
      Table 1APOE gene mutations reported with dyslipoproteinemias.
      rs numbercDNA position*Protein position*SegregationCommon nameTransmissionPhenotypeRef.
      -c.15G > Ap.Trp5*2 familiesFD (RP)[
      • Leren T.P.
      • Strøm T.B.
      • Berge K.E.
      Variable phenotypic expression of nonsense mutation p.Thr5* in the APOE gene.
      ]
      rs121918392c.61G > Ap.Glu21Lys2 casesApoE5HC[
      • Wardell M.R.
      • Rall S.C.
      • Schaefer E.J.
      • Kane J.P.
      • Weisgraber K.H.
      Two apolipoprotein E5 variants illustrate the importance of the position of additional positive charge on receptor-binding activity.
      ,
      • Mailly F.
      • Xu C.F.
      • Xhignesse M.
      • Lussier-Cacan S.
      • Talmud P.J.
      • Davignon J.
      • et al.
      Characterization of a new apolipoprotein E5 variant detected in two French-Canadian subjects.
      ]
      rs121918392c.61G > A-E2p.Glu21Lys-E21 caseApoE5-ApoE2LPG[
      • Miyata T.
      • Sugiyama S.
      • Nangaku M.
      • Suzuki D.
      • Uragami K.
      • Inagi R.
      • et al.
      Apolipoprotein E2/E5 variants in lipoprotein glomerulopathy recurred in transplanted kidney.
      ]
      rs201672011/rs769455c.91G > A/c.487C > Tp.Glu31Lys/p.Arg163Cys1 family, 6 htz, 1 hmzPhiladelphiaFD[
      • Lohse P.
      • Rader D.J.
      • Brewer H.B.
      Heterozygosity for apolipoprotein E-4Philadelphia(Glu13–--Lys, Arg145–--Cys) is associated with incomplete dominance of type III hyperlipoproteinemia.
      ]
      CM980097c.114G > A-E2p.Trp38*-E21 caseFD[
      • Feussner G.
      • Feussner V.
      • Hoffmann M.M.
      • Lohrmann J.
      • Wieland H.
      • März W.
      Molecular basis of type III hyperlipoproteinemia in Germany.
      ]
      rs121918399c.127C > Tp.Arg43Cys6 individual cases, 2 familiesKyotoLPG[
      • Yang M.
      • Weng Q.
      • Pan X.
      • Hussain H.M.J.
      • Yu S.
      • Xu J.
      • et al.
      Clinical and genetic analysis of lipoprotein glomerulopathy patients caused by APOE mutations.
      ,
      • Matsunaga A.
      • Sasaki J.
      • Komatsu T.
      • Kanatsu K.
      • Tsuji E.
      • Moriyama K.
      • et al.
      A novel apolipoprotein E mutation, E2 (Arg25Cys), in lipoprotein glomerulopathy.
      ,
      • Rovin B.H.
      • Roncone D.
      • McKinley A.
      • Nadasdy T.
      • Korbet S.M.
      • Schwartz M.M.
      APOE Kyoto mutation in European Americans with lipoprotein glomerulopathy.
      ]
      rs769452c.137T > Cp.Leu46Pro1 caseHC[
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ]
      -c.146delGp.Gly49Valfs*292 family membersFD[
      • Feussner G.
      • Funke H.
      • Weng W.
      • Assmann G.
      • Lackner K.J.
      • Ziegler R.
      Severe type III hyperlipoproteinemia associated with unusual apolipoprotein E1 phenotype and epsilon 1/’null’ genotype.
      ]
      -/rs267606664c.146delG/c.434G > A-E2p.Gly49Valfs*29/p.Gly145Asp-E21 caseFD[
      • Feussner G.
      • Funke H.
      • Weng W.
      • Assmann G.
      • Lackner K.J.
      • Ziegler R.
      Severe type III hyperlipoproteinemia associated with unusual apolipoprotein E1 phenotype and epsilon 1/’null’ genotype.
      ]
      rs370594287c.192G > Cp.Gln64His1 caseFD[
      • Matsunaga A.
      • Sasaki J.
      • Komatsu T.
      • Kanatsu K.
      • Tsuji E.
      • Moriyama K.
      • et al.
      A novel apolipoprotein E mutation, E2 (Arg25Cys), in lipoprotein glomerulopathy.
      ]
      rs1180612218c.295C > A-E4p.Gln99Lys-E41 caseFrankfurt, ApoE5HC[
      • Ruzicka V.
      • März W.
      • Russ A.
      • Fisher E.
      • Mondorf W.
      • Gross W.
      Characterization of the gene for apolipoprotein E5-Frankfurt (Gln81->Lys, Cys112->Arg) by polymerase chain reaction, restriction isotyping, and temperature gradient gel electrophoresis.
      ]
      rs11083750c.305C > Gp.Pro102Arg1 caseApoE5HC[
      • Wardell M.R.
      • Rall S.C.
      • Schaefer E.J.
      • Kane J.P.
      • Weisgraber K.H.
      Two apolipoprotein E5 variants illustrate the importance of the position of additional positive charge on receptor-binding activity.
      ]
      -c.339dupGp.Glu114Glyfs*501 familyGroningendominantFD[
      • Dijck-Brouwer D.A.J.
      • van Doormaal J.J.
      • Kema I.P.
      • Brugman A.M.
      • Kingma A.W.
      • Muskiet F.A.J.
      Discovery and consequences of apolipoprotein-epsilon(3Groningen): a G-insertion in codon 95/96 that is predicted to cause a premature stop codon.
      ]
      rs11542041c.394C > Tp.Arg132Cys1 caseTsukubaLPG[
      • Hagiwara M.
      • Yamagata K.
      • Matsunaga T.
      • Arakawa Y.
      • Usui J.
      • Shimizu Y.
      • et al.
      A novel apolipoprotein E mutation, ApoE Tsukuba (Arg 114 Cys), in lipoprotein glomerulopathy.
      ]
      rs397514254c.415_435dup21-E4p.Glu139_Gly145dup-E41 familyLeidendominantFD[
      • Havekes L.
      • de Wit E.
      • Leuven J.G.
      • Klasen E.
      • Utermann G.
      • Weber W.
      • et al.
      Apolipoprotein E3-Leiden. A new variant of human apolipoprotein E associated with familial type III hyperlipoproteinemia.
      ,
      • Richard P.
      • Beucler I.
      • Pascual De Zulueta M.
      • Biteau N.
      • De Gennes J.L.
      • Iron A.
      Compound heterozygote for both rare apolipoprotein E1 (Gly127-->Asp, Arg158-->Cys) and E3(Cys112-->Arg, Arg251-->Gly) alleles in a multigeneration pedigree with hyperlipoproteinaemia.
      ]
      rs267606664c.434G > A-E2p.Gly145Asp-E21 family, 3 casesMixed (RP), FD[
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ,
      • Civeira F.
      • Pocoví M.
      • Cenarro A.
      • Casao E.
      • Vilella E.
      • Joven J.
      • et al.
      Apo E variants in patients with type III hyperlipoproteinemia.
      ]
      rs267606664c.434G > Ap.Gly145Asp9 family membersdominantFD[
      • Richard P.
      • Beucler I.
      • Pascual De Zulueta M.
      • Biteau N.
      • De Gennes J.L.
      • Iron A.
      Compound heterozygote for both rare apolipoprotein E1 (Gly127-->Asp, Arg158-->Cys) and E3(Cys112-->Arg, Arg251-->Gly) alleles in a multigeneration pedigree with hyperlipoproteinaemia.
      ]
      rs267606664/rs267606661c.434G > A/c.805C > Gp.Gly145Asp/p.Arg269Gly1 caseFD[
      • Richard P.
      • Beucler I.
      • Pascual De Zulueta M.
      • Biteau N.
      • De Gennes J.L.
      • Iron A.
      Compound heterozygote for both rare apolipoprotein E1 (Gly127-->Asp, Arg158-->Cys) and E3(Cys112-->Arg, Arg251-->Gly) alleles in a multigeneration pedigree with hyperlipoproteinaemia.
      ]
      -c.457_480dup24p.Val153_Arg160dup1 caseApoE5ssHTG[
      • Yamanouchi Y.
      • Takano T.
      • Hamaguchi H.
      • Tokunaga K.
      A novel apolipoprotein E5 variant with a 24-bp insertion causing hyperlipidemia.
      ]
      rs121918393c.460C > Tp.Arg154Cys1 familydominantFD[
      • Feussner G.
      • Albanese M.
      • Mann W.A.
      • Valencia A.
      • Schuster H.
      Apolipoprotein E2 (Arg-136-->Cys), a variant of apolipoprotein E associated with late-onset dominance of type III hyperlipoproteinaemia.
      ]
      rs121918393c.460C > Ap.Arg154Ser15 cases, 3 familiesChristchurchdominantFD (RP), FCHL, HTG[
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ,
      • Wardell M.R.
      • Brennan S.O.
      • Janus E.D.
      • Fraser R.
      • Carrell R.W.
      Apolipoprotein E2-Christchurch (136 Arg–--Ser). New variant of human apolipoprotein E in a patient with type III hyperlipoproteinemia.
      ,
      • Pocovi M.
      • Cenarro A.
      • Civeira F.
      • Myers R.H.
      • Casao E.
      • Esteban M.
      • et al.
      Incomplete dominance of type III hyperlipoproteinemia is associated with the rare apolipoprotein E2 (Arg136-->Ser) variant in multigenerational pedigree studies.
      ,
      • Civeira F.
      • Pocoví M.
      • Cenarro A.
      • Casao E.
      • Vilella E.
      • Joven J.
      • et al.
      Apo E variants in patients with type III hyperlipoproteinemia.
      ,
      • Lamiquiz-Moneo I.
      • Blanco-Torrecilla C.
      • Bea A.M.
      • Mateo-Gallego R.
      • Pérez-Calahorra S.
      • Baila-Rueda L.
      • et al.
      Frequency of rare mutations and common genetic variations in severe hypertriglyceridemia in the general population of Spain.
      ]
      CM950078c.461G > Ap.Arg154His9 family membersrecessive?HTG[
      • Minnich A.
      • Weisgraber K.H.
      • Newhouse Y.
      • Dong L.M.
      • Fortin L.J.
      • Tremblay M.
      • et al.
      Identification and characterization of a novel apolipoprotein E variant, apolipoprotein E3’ (Arg136-->His): association with mild dyslipidemia and double pre-beta very low density lipoproteins.
      ]
      rs121918393c.460C > T-E2p.Arg154Cys-E23 families, 1 caseFD[
      • Emi M.
      • Wu L.L.
      • Robertson M.A.
      • Myers R.L.
      • Hegele R.A.
      • Williams R.R.
      • et al.
      Genotyping and sequence analysis of apolipoprotein E isoforms.
      ,
      • Walden C.C.
      • Huff M.W.
      • Leiter L.A.
      • Connelly P.W.
      • Hegele R.A.
      Detection of a new apolipoprotein-E mutation in type III hyperlipidemia using deoxyribonucleic acid restriction isotyping.
      ,
      • Rolleri M.
      • Vivona N.
      • Emmanuele G.
      • Cefalù A.B.
      • Pisciotta L.
      • Guido V.
      • et al.
      Two Italian kindreds carrying the Arg136-->Ser mutation of the Apo E gene: development of premature and severe atherosclerosis in the presence of epsilon 2 as second allele.
      ]
      -p.Leu159_Lys161del1 caseTokyoLPG[
      • Konishi K.
      • Saruta T.
      • Kuramochi S.
      • Oikawa S.
      • Saito T.
      • Han H.
      • et al.
      Association of a novel 3-amino acid deletion mutation of apolipoprotein E (Apo E Tokyo) with lipoprotein glomerulopathy.
      ]
      CM043808c.478C > Ap.Arg160Ser1 caseFD[
      • Maruyama T.
      • Yamashita S.
      • Matsuzawa Y.
      • Bujo H.
      • Takahashi K.
      • Saito Y.
      • et al.
      Mutations in Japanese subjects with primary hyperlipidemia–results from the Research committee of the ministry of health and welfare of Japan since 1996–.
      ]
      CM950079c.479G > Tp.Arg160Leu2 family membersFD[
      • Richard P.
      • de Zulueta M.P.
      • Beucler I.
      • De Gennes J.L.
      • Cassaigne A.
      • Iron A.
      Identification of a new apolipoprotein E variant (E2 Arg142-->Leu) in type III hyperlipidemia.
      ]
      CM890009c.478C > T-E4p.Arg160Cys-E46 family membersdominantFD[
      • Rall S.C.
      • Newhouse Y.M.
      • Clarke H.R.
      • Weisgraber K.H.
      • McCarthy B.J.
      • Mahley R.W.
      • et al.
      Type III hyperlipoproteinemia associated with apolipoprotein E phenotype E3/3. Structure and genetics of an apolipoprotein E3 variant.
      ]
      -p. Arg160_Leu162del1 caseMaebashiLPG[
      • Ogawa T.
      • Maruyama K.
      • Hattori H.
      • Arai H.
      • Kondoh I.
      • Egashira T.
      • et al.
      A new variant of apolipoprotein E (apo E Maebashi) in lipoprotein glomerulopathy.
      ]
      -c.477_491del15p.Lys161_Arg165 del5 family membersLPG (RP)[
      • Xie W.
      • Xie Y.
      • Lin Z.
      • Xu X.
      • Zhang Y.
      A novel apolipoprotein E mutation caused by a five amino acid deletion in a Chinese family with lipoprotein glomerulopathy: a case report.
      ]
      -c.484_492del9p.Leu162_Lys164del1 caseFD[
      • Konishi K.
      • Saruta T.
      • Kuramochi S.
      • Oikawa S.
      • Saito T.
      • Han H.
      • et al.
      Association of a novel 3-amino acid deletion mutation of apolipoprotein E (Apo E Tokyo) with lipoprotein glomerulopathy.
      ]
      rs769455c.487C > Tp.Arg163Cys1 family, 1 htz and 1 hmzADH[
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ]
      rs769455c.487C > T-E2p.Arg163Cys-E243 cases, 39 htz, 4 hmz, 1 familydominantFD (RP)[
      • de Villiers W.J.
      • van der Westhuyzen D.R.
      • Coetzee G.A.
      • Henderson H.E.
      • Marais A.D.
      The apolipoprotein E2 (Arg145Cys) mutation causes autosomal dominant type III hyperlipoproteinemia with incomplete penetrance.
      ,
      • Emi M.
      • Wu L.L.
      • Robertson M.A.
      • Myers R.L.
      • Hegele R.A.
      • Williams R.R.
      • et al.
      Genotyping and sequence analysis of apolipoprotein E isoforms.
      ]
      rs121918397c.488G > Ap.Arg163His1 family, 1 caseKochiHTG, FD[
      • Maruyama T.
      • Yamashita S.
      • Matsuzawa Y.
      • Bujo H.
      • Takahashi K.
      • Saito Y.
      • et al.
      Mutations in Japanese subjects with primary hyperlipidemia–results from the Research committee of the ministry of health and welfare of Japan since 1996–.
      ,
      • Hidaka H.
      • Tozuka M.
      • Hidaka E.
      • Yamauchi K.
      • Ota H.
      • Honda T.
      • et al.
      Characterization of an apolipoprotein E3 variant (Arg 145-->His) associated with mild hypertriglyceridemia.
      ]
      CM972792c.488G > Cp.Arg163Pro3 casesSendaiLPG[
      • Oikawa S.
      • Matsunaga A.
      • Saito T.
      • Sato H.
      • Seki T.
      • Hoshi K.
      • et al.
      Apolipoprotein E Sendai (arginine 145-->proline): a new variant associated with lipoprotein glomerulopathy.
      ]
      CM972792/rs121918392c.488G > C/c.61G > Ap.Arg163Pro/p.Glu21Lys1 caseSendai/ApoE5LPG[
      • Takasaki S.
      • Matsunaga A.
      • Joh K.
      • Saito T.
      A case of lipoprotein glomerulopathy with a rare apolipoprotein E isoform combined with neurofibromatosis type I.
      ]
      CM890010c.490A > Gp.Lys164Glu2 families, 1 caseApoE1dominantFD (RP)[
      • Moriyama K.
      • Sasaki J.
      • Matsunaga A.
      • Arakawa F.
      • Takada Y.
      • Araki K.
      • et al.
      Apolipoprotein E1 Lys-146–--Glu with type III hyperlipoproteinemia.
      ,
      • Mann W.A.
      • Lohse P.
      • Gregg R.E.
      • Ronan R.
      • Hoeg J.M.
      • Zech L.A.
      • et al.
      Dominant expression of type III hyperlipoproteinemia. Pathophysiological insights derived from the structural and kinetic characteristics of ApoE-1 (Lys146-->Glu).
      ,
      • Visser M.E.
      • Dallinga-Thie G.M.
      • Pinto-Sietsma S.J.
      • Defesche J.C.
      • Stroes E.S.
      • van der Valk P.R.
      APOE1 mutation in a patient with type III hyperlipoproteinaemia: detailed genetic analysis required.
      ]
      rs121918394c.490A > G-E2p.Lys164Gln-E23 familiesdominantFD[
      • Rall S.C.
      • Weisgraber K.H.
      • Innerarity T.L.
      • Bersot T.P.
      • Mahley R.W.
      • Blum C.B.
      Identification of a new structural variant of human apolipoprotein E, E2(Lys146 leads to Gln), in a type III hyperlipoproteinemic subject with the E3/2 phenotype.
      ,
      • Smit M.
      • de Knijff P.
      • van der Kooij-Meijs E.
      • Groenendijk C.
      • van den Maagdenberg A.M.
      • Gevers Leuven J.A.
      • et al.
      Genetic heterogeneity in familial dysbetalipoproteinemia. The E2(lys146–--gln) variant results in a dominant mode of inheritance.
      ]
      rs121918394c.490A > C-E2p.Lys164Glu-E25 family membersHarrisburgdominantFD[
      • Mann W.A.
      • Gregg R.E.
      • Sprecher D.L.
      • Brewer H.B.
      Apolipoprotein E-1Harrisburg: a new variant of apolipoprotein E dominantly associated with type III hyperlipoproteinemia.
      ]
      −/−c.492G > C/c.493C > Tp.Lys164Asn/p.Arg165Trp3 family membersHammersmithdominantFD[
      • Hoffer M.J.
      • Niththyananthan S.
      • Naoumova R.P.
      • Kibirige M.S.
      • Frants R.R.
      • Havekes L.M.
      • et al.
      Apolipoprotein E1-Hammersmith (Lys146-->Asn;Arg147-->Trp), due to a dinucleotide substitution, is associated with early manifestation of dominant type III hyperlipoproteinaemia.
      ]
      CM064979c.494G > Cp.Arg165Pro2 casesChicagoLPG[
      • Yang M.
      • Weng Q.
      • Pan X.
      • Hussain H.M.J.
      • Yu S.
      • Xu J.
      • et al.
      Clinical and genetic analysis of lipoprotein glomerulopathy patients caused by APOE mutations.
      ,
      • Sam R.
      • Wu H.
      • Yue L.
      • Mazzone T.
      • Schwartz M.M.
      • Arruda J.A.L.
      • et al.
      Lipoprotein glomerulopathy: a new apolipoprotein E mutation with enhanced glomerular binding.
      ]
      CM064979/rs121918392c.494G > C/c.61G > Ap.Arg165Pro/p.Glu21Lys1 caseChicago/ApoE5LPG[
      • Kodera H.
      • Mizutani Y.
      • Sugiyama S.
      • Miyata T.
      • Ehara T.
      • Matsunaga A.
      • et al.
      A case of lipoprotein glomerulopathy with apoE chicago and apoE (Glu3Lys) treated with fenofibrate.
      ]
      rs746494694c.500_502delTCCp.Leu167del2 ADH families, 11 cases, 3 FCHL familiesdominantADH, HC, FCHL[
      • Cenarro A.
      • Etxebarria A.
      • de Castro-Orós I.
      • Stef M.
      • Bea A.M.
      • Palacios L.
      • et al.
      The p.Leu167del Mutation in APOE Gene Causes Autosomal Dominant Hypercholesterolemia by Down-regulation of LDL Receptor Expression in Hepatocytes.
      ,
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ,
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ,
      • Faivre L.
      • Saugier-Veber P.
      • Pais de Barros J.-P.
      • Verges B.
      • Couret B.
      • Lorcerie B.
      • et al.
      Variable expressivity of the clinical and biochemical phenotype associated with the apolipoprotein E p.Leu149del mutation.
      ,
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ]
      CM087959c.502C > Tp.Arg168Cys1 case, 1 familyModena, ShenzhenLPG (RP)[
      • Ku M.
      • Tao C.
      • Zhou A.-A.
      • Cheng Y.
      • Wan Q.-J.
      A novel apolipoprotein E mutation (p.Arg150Cys) in a Chinese patient with lipoprotein glomerulopathy.
      ,
      • Cautero N.
      • Di Benedetto F.
      • De Ruvo N.
      • Montalti R.
      • Guerrini G.P.
      • Ballarin R.
      • et al.
      Novel genetic mutation in apolipoprotein E2 homozygosis and its implication in organ donation: a case report.
      ]
      CM075988c.503G > Cp.Arg168Pro1 familyGuangzhouLPG (RP)[
      • Luo B.
      • Huang F.
      • Liu Q.
      • Li X.
      • Chen W.
      • Zhou S.-F.
      • et al.
      Identification of apolipoprotein E Guangzhou (arginine 150 proline), a new variant associated with lipoprotein glomerulopathy.
      ]
      CM104291c.509C > Ap.Ala170Asp1 caseLas VegasLPG[
      • Bomback A.S.
      • Song H.
      • D'Agati V.D.
      • Cohen S.D.
      • Neal A.
      • Appel G.B.
      • et al.
      A new apolipoprotein E mutation, apoE Las Vegas, in a European-American with lipoprotein glomerulopathy.
      ]
      CM088091c.502C > G-E2/E2p.Arg168Gly-E2/E21 caseOkayama, ApoE1LPG[
      • Kinomura M.
      • Sugiyama H.
      • Saito T.
      • Matsunaga A.
      • Sada K.
      • Kanzaki M.
      • et al.
      A novel variant apolipoprotein E Okayama in a patient with lipoprotein glomerulopathy.
      ]
      -c.518T > Cp.Leu173Pro2 family membersChengduLPG[
      • Wu H.
      • Yang Y.
      • Hu Z.
      The novel apolipoprotein E mutation ApoE chengdu (c.518T>C, p.L173P) in a Chinese patient with lipoprotein glomerulopathy.
      ]
      -c.520-573del54p.Gln174_Gly190del2 family membersApoE1LPG[
      • Ando M.
      • Sasaki J.
      • Hua H.
      • Matsunaga A.
      • Uchida K.
      • Jou K.
      • et al.
      A novel 18-amino acid deletion in apolipoprotein E associated with lipoprotein glomerulopathy.
      ]
      rs7412c.526C > Tp.Arg176CyshmzApoE2recessiveFD[
      • Rall S.C.
      • Weisgraber K.H.
      • Innerarity T.L.
      • Mahley R.W.
      Structural basis for receptor binding heterogeneity of apolipoprotein E from type III hyperlipoproteinemic subjects.
      ]
      CM111115c.527G > Cp.Arg176Pro7 casesOsaka/KurashikiLPG[
      • Yang M.
      • Weng Q.
      • Pan X.
      • Hussain H.M.J.
      • Yu S.
      • Xu J.
      • et al.
      Clinical and genetic analysis of lipoprotein glomerulopathy patients caused by APOE mutations.
      ,
      • Saito T.
      • Matsunaga A.
      Significance of a novel apolipoprotein E variant, ApoE Osaka/Kurashiki, in lipoprotein glomerulopathy.
      ,
      • Yang Z.
      • Wu H.
      • Hu Z.
      [Discovery of a Chinese Tibetan patient with lipoprotein glomerulopathy due to APOE Osaka/Kurashiki variant].
      ]
      CM111115c.527G > C-E2p.Arg176Pro-E22 casesOsaka/KurashikiLPG[
      • Mitani A.
      • Ishigami M.
      • Watase K.
      • Minakata T.
      • Yamamura T.
      A novel apolipoprotein E mutation, ApoE Osaka (Arg158 Pro), in a dyslipidemic patient with lipoprotein glomerulopathy.
      ,
      • Tokura T.
      • Itano S.
      • Kobayashi S.
      • Kuwabara A.
      • Fujimoto S.
      • Horike H.
      • et al.
      A novel mutation ApoE2 Kurashiki (R158P) in a patient with lipoprotein glomerulopathy.
      ]
      rs1426426514c.592C > Tp.Arg198Cys1 caseBadenHTG[
      • Hoffmann M.M.
      • Scharnagl H.
      • Köster W.
      • Winkler K.
      • Wieland H.
      • März W.
      Apolipoprotein E1 Baden (Arg(180)-->Cys). A new apolipoprotein E variant associated with hypertriglyceridemia.
      ]
      CM980098c.613C > Gp.Gln205Glu1 caseToranomonFD[
      • Okubo M.
      • Aoyama Y.
      • Harada K.
      • Fukawa M.
      • Tsukada T.
      • Mokuno H.
      • et al.
      A novel apolipoprotein E2 variant, E2Toranomon (Q187E), identified in a type III hyperlipoproteinemia patient with coronary atherosclerosis.
      ]
      -c.644C > G-E2/E2p.Ser215Cys-E2/E23 caseToyonakaLPG, FD[
      • Kato T.
      • Ushiogi Y.
      • Yokoyama H.
      • Hara S.
      • Matsunaga A.
      • Muso E.
      • et al.
      A case of apolipoprotein E Toyonaka and homozygous apolipoprotein E2/2 showing non-immune membranous nephropathy-like glomerular lesions with foamy changes.
      ,
      • Fukunaga M.
      • Nagahama K.
      • Aoki M.
      • Shimizu A.
      • Hara S.
      • Matsunaga A.
      • et al.
      Membranous nephropathy-like apolipoprotein E deposition disease with apolipoprotein E Toyonaka (Ser197Cys) and a homozygous apolipoprotein E2/2.
      ,
      • Hirashima H.
      • Komiya T.
      • Toriu N.
      • Hara S.
      • Matsunaga A.
      • Saito T.
      • et al.
      A case of nephrotic syndrome showing contemporary presence of apolipoprotein E2 homozygote glomerulopathy and membranous nephropathy-like findings modified by apolipoprotein E Toyonaka.
      ]
      CD961785c.679_688del10p.Ala227Glyfs*201 family, 10 htz and 1 hmzdominantFD[
      • Feussner G.
      • Dobmeyer J.
      • Gröne H.J.
      • Lohmer S.
      • Wohlfeil S.A.
      10-bp deletion in the apolipoprotein epsilon gene causing apolipoprotein E deficiency and severe type III hyperlipoproteinemia.
      ]
      rs121918396c.683G > Ap.Trp228*1 family, 2 htz and 1 hmzWashingtondominantFD[
      • Lohse P.
      • Brewer H.B.
      • Meng M.S.
      • Skarlatos S.I.
      • LaRosa J.C.
      • Brewer H.B.
      Familial apolipoprotein E deficiency and type III hyperlipoproteinemia due to a premature stop codon in the apolipoprotein E gene.
      ]
      rs567353589c.688G > Ap.Glu230Lys1 family (6 htz, 2 hmz)ApoE5dominantFCHL[
      • Feussner G.
      • Scharnagl H.
      • Scherbaum C.
      • Acar J.
      • Dobmeyer J.
      • Lohrmann J.
      • et al.
      Apolipoprotein E5 (Glu212-->Lys): increased binding to cell surface proteoglycans but decreased uptake and lysosomal degradation in cultured fibroblasts.
      ]
      CD961785c.701C > Tp.Ala234Val1 caseNananumaFD[
      • Maruyama T.
      • Yamashita S.
      • Matsuzawa Y.
      • Bujo H.
      • Takahashi K.
      • Saito Y.
      • et al.
      Mutations in Japanese subjects with primary hyperlipidemia–results from the Research committee of the ministry of health and welfare of Japan since 1996–.
      ]
      rs530010303c.703C > Tp.Arg235Trp1 casemixed[
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ]
      rs267606663c.725G > Ap.Arg242Gln1 caseFukuokamixed[
      • Moriyama K.
      • Sasaki J.
      • Takada Y.
      • Arakawa F.
      • Matsunaga A.
      • Ito Y.
      • et al.
      Characterization of a novel variant of apolipoprotein E, E2 Fukuoka (Arg-224--> Gln) in a hyperlipidemic patient with xanthomatosis.
      ]
      rs267606664c.434G > A-E2p.Gly145Asp-E23 family membersFD[
      • Feussner G.
      • Funke H.
      • Weng W.
      • Assmann G.
      • Lackner K.J.
      • Ziegler R.
      Severe type III hyperlipoproteinemia associated with unusual apolipoprotein E1 phenotype and epsilon 1/’null’ genotype.
      ]
      rs121918395c.736C > T-E2p.Arg246Cys-E2twinsDunedinHTG[
      • van den Maagdenberg A.M.
      • Weng W.
      • de Bruijn I.H.
      • de Knijff P.
      • Funke H.
      • Smelt A.H.
      • et al.
      Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.
      ]
      -/rs121918399c.742G > T/c.127C > Tp.Asp248Tyr/p.Arg43Cys1 caseHong Kong/KyotoLPG[
      • Cheung C.Y.
      • Chan A.O.K.
      • Chan Y.H.
      • Lee K.C.
      • Chan G.P.T.
      • Lau G.T.C.
      • et al.
      A rare cause of nephrotic syndrome: lipoprotein glomerulopathy.
      ]
      rs199768005c.761T > A-E2p.Val254Glu-E21 casemixed[
      • van den Maagdenberg A.M.
      • Weng W.
      • de Bruijn I.H.
      • de Knijff P.
      • Funke H.
      • Smelt A.H.
      • et al.
      Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.
      ]
      rs140808909/rs190853081c.784G > A/c.787G > Ap.Glu262Lys/p.Glu263Lys14 casesSuita/ApoE7HC, mixed, HTG[
      • Maeda H.
      • Nakamura H.
      • Kobori S.
      • Okada M.
      • Mori H.
      • Niki H.
      • et al.
      Identification of human apolipoprotein E variant gene: apolipoprotein E7 (Glu244,245–--Lys244,245).
      ,
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ,
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ,
      • Tsuchiya S.
      • Yamanouchi Y.
      • Miyazaki R.
      • Yanagi H.
      • Yamakawa K.
      • Yuzawa K.
      • et al.
      Association of the apolipoprotein E4 allele with hypercholesterolemia in apparently healthy male adults in Tokyo.
      ,
      • Kitahara M.
      • Shinomiya M.
      • Shirai K.
      • Saito Y.
      • Yoshida S.
      Frequency and role of apo E phenotype in familial hypercholesterolemia and non-familial hyperlipidemia in the Japanese.
      ,
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      rs267606661c.805C > Gp.Arg269Gly1 case, 1 familyHTG, FD[
      • van den Maagdenberg A.M.
      • Weng W.
      • de Bruijn I.H.
      • de Knijff P.
      • Funke H.
      • Smelt A.H.
      • et al.
      Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.
      ,
      • Richard P.
      • Beucler I.
      • Pascual De Zulueta M.
      • Biteau N.
      • De Gennes J.L.
      • Iron A.
      Compound heterozygote for both rare apolipoprotein E1 (Gly127-->Asp, Arg158-->Cys) and E3(Cys112-->Arg, Arg251-->Gly) alleles in a multigeneration pedigree with hyperlipoproteinaemia.
      ]
      rs267606661c.805C > Gp.Arg269Gly1 casetype IIa[
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ]
      -c.808C > G-c.809T > A-E2p.Leu270Glu-E21 casetype IIa[
      • van den Maagdenberg A.M.
      • Weng W.
      • de Bruijn I.H.
      • de Knijff P.
      • Funke H.
      • Smelt A.H.
      • et al.
      Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.
      ]
      * Transcipt ENST00000252486.9 (Ensembl Reference Sequence), NM_000041.4 (NCBI Reference Sequence).
      Htz: heterozygote. Hmz: homozygote.
      ADH: autosomal dominant hypercholeterolemia (Type IIa). FCHL: familial combined hyperlipidemia (type IIb). FD: familial dysbetalipoproteinemia (type III). LPG: lipoprotein glomerulopathy. HTG: hypertriglyceridemia (Type IV and V). HC: hypercholesterolemia. RP: reduced penetrance.
      Moreover, rare apoE mutants have been associated with different dyslipidemias such as familial dysbetalipoproteinemia (FD, type III) (OMIM # 617347), familial combined hyperlipidaemia (FCHL, type IIb) (OMIM # 144250), ADH (type IIa), hypertriglyceridemia (HTG, type IV and V), lipoprotein glomerulopathy (LPG) (OMIM #611771) [
      • Saito T.
      • Matsunaga A.
      • Fukunaga M.
      • Nagahama K.
      • Hara S.
      • Muso E.
      Apolipoprotein E-related glomerular disorders.
      ,
      • Yang M.
      • Weng Q.
      • Pan X.
      • Hussain H.M.J.
      • Yu S.
      • Xu J.
      • et al.
      Clinical and genetic analysis of lipoprotein glomerulopathy patients caused by APOE mutations.
      ], sea-blue histiocytosis (OMIM #269600) [
      • Nguyen T.T.
      • Kruckeberg K.E.
      • O'Brien J.F.
      • Ji Z.-S.
      • Karnes P.S.
      • Crotty T.B.
      • et al.
      Familial splenomegaly: macrophage hypercatabolism of lipoproteins associated with apolipoprotein E mutation [apolipoprotein E (Δ149 leu)].
      ] or late-onset Alzheimer disease (OMIM # 104310) [
      • Rasmussen K.L.
      • Tybjaerg-Hansen A.
      • Nordestgaard B.G.
      • Frikke-Schmidt R.
      APOE and dementia - resequencing and genotyping in 105,597 individuals.
      ].

      2. ApoE and autosomal dominant hypercholesterolemia (ADH)

      Familial Hypercholesterolemia (FH) is an autosomal codominant genetic lipoprotein disorder, type IIa hyperlipoproteinemia according to Fredrickson's classification [
      • Fredrickson D.S.
      • Levy R.I.
      • Lees R.S.
      Fat transport in lipoproteins–an integrated approach to mechanisms and disorders.
      ,
      • Beaumont J.L.
      • Carlson L.A.
      • Cooper G.R.
      • Fejfar Z.
      • Fredrickson D.S.
      • Strasser T.
      Classification of hyperlipidaemias and hyperlipoproteinaemias.
      ], initially identified through mutations into the low density lipoprotein receptor encoded by the LDLR gene at 19p13.2 (OMIM #143890, #606945). FH is a codominant disease since each allele contributes to the phenotype and heterozygotes present with an intermediate phenotype of that of homozygotes. The same phenotype is also observed with mutations in the apolipoprotein B [APOB gene at 2p24.1 (familial defective apolipoprotein B (OMIM #107730, #144010))], the proprotein convertase subtilisin/kexin type 9 [PCSK9 gene at 1p32.3 (OMIM # 607786)] - and the apolipoprotein E [APOE gene at 19q13.32 (OMIM #107741)]. While homozygous carriers of an APOB mutation are very rare, Familial defective apolipoprotein B appears to be a dominant disease with homozygotes reported to have cholesterol concentrations in the range for heterozygotes carriers [
      • Andersen L.H.
      • Miserez A.R.
      • Ahmad Z.
      • Andersen R.L.
      Familial defective apolipoprotein B-100: a review.
      ]. To our knowledge, no homozygous carrier of a PCSK9 or APOE hypercholesterolemic mutation has been reported yet, thus the status of the transmission mode for these diseases cannot be defined as dominant or codominant. Nowadays, frequently the denomination FH is used for all these forms of type IIa hyperlipoproteinemia while the most suitable denomination is Autosomal Dominant Hypercholesterolemia (ADH) as FH refers to LDLR mutation carriers only. There is the need of an international consensus on precise terminology to avoid misunderstanding.
      ADH is one of the most frequent genetic diseases with a prevalence of 1 in 313 or 311 according to two recent meta-analyses of 11 [
      • Beheshti S.O.
      • Madsen C.M.
      • Varbo A.
      • Nordestgaard B.G.
      Worldwide prevalence of familial hypercholesterolemia: meta-analyses of 11 million subjects.
      ] and 7.3 [
      • Hu P.
      • Dharmayat K.I.
      • Stevens C.A.T.
      • Sharabiani M.T.A.
      • Jones R.S.
      • Watts G.F.
      • et al.
      Prevalence of familial hypercholesterolemia among the general population and patients with atherosclerotic cardiovascular disease: a systematic review and meta-analysis.
      ] million subjects. ADH is characterized by a selective increase of circulating Low Density Lipoproteins (LDL) in the plasma since birth giving rise to premature mortality from cardiovascular disease (CVD), with a 13-fold higher coronaropathy risk [
      • Benn M.
      • Watts G.F.
      • Tybjaerg-Hansen A.
      • Nordestgaard B.G.
      Familial hypercholesterolemia in the Danish general population: prevalence, coronary artery disease, and cholesterol-lowering medication.
      ]. ADH has proven to be genetically heterogeneous and associated with defects in at least four different genes. In 1973, Goldstein et al. showed that ADH may result from defects in the LDL receptor that removes LDL from plasma [
      • Goldstein J.L.
      • Schrott H.G.
      • Hazzard W.R.
      • Bierman E.L.
      • Motulsky A.G.
      Hyperlipidemia in coronary heart disease. II. Genetic analysis of lipid levels in 176 families and delineation of a new inherited disorder, combined hyperlipidemia.
      ]. Subsequently, Innerarity et al. revealed the genetic heterogeneity of ADH by reporting hypercholesterolemic patients with normal LDL receptor activity [
      • Innerarity T.L.
      • Weisgraber K.H.
      • Arnold K.S.
      • Mahley R.W.
      • Krauss R.M.
      • Vega G.L.
      • et al.
      Familial defective apolipoprotein B-100: low density lipoproteins with abnormal receptor binding.
      ]. Their work on these patients led to the detection of the first hypercholesterolemic mutation in the APOB gene, which encodes the main ligand for the LDL receptor: apolipoprotein B-100 (apo B-100) implicated in the uptake of LDL particles from blood [
      • Soria L.F.
      • Ludwig E.H.
      • Clarke H.R.
      • Vega G.L.
      • Grundy S.M.
      • McCarthy B.J.
      Association between a specific apolipoprotein B mutation and familial defective apolipoprotein B-100.
      ]. Fourteen years later, gain of function mutations in PCSK9 (proprotein convertase subtilysin kexin 9) were reported in ADH families unlinked to either the LDLR or the APOB gene [
      • Abifadel M.
      • Varret M.
      • Rabes J.-P.
      • Allard D.
      • Ouguerram K.
      • Devillers M.
      • et al.
      Mutations in PCSK9 cause autosomal dominant hypercholesterolemia.
      ]. PCSK9, the ninth member of the proprotein convertase (PC) family, has been identified as a major regulator of cholesterol homeostasis [
      • Blanchard V.
      • Khantalin I.
      • Ramin-Mangata S.
      • Chémello K.
      • Nativel B.
      • Lambert G.
      PCSK9: from biology to clinical applications.
      ]. PCSK9 binds the extracellular epidermal growth factor-like repeat A (EGF-A) domain of the LDL receptor and thus disrupts its recycling to the cell surface by targeting it to the lysosomal pathway for degradation [
      • Seidah N.G.
      • Abifadel M.
      • Prost S.
      • Boileau C.
      • Prat A.
      The proprotein convertases in hypercholesterolemia and cardiovascular diseases: emphasis on proprotein convertase subtilisin/kexin 9.
      ]. Further genetic heterogeneity of ADH has been established more recently, with the demonstration that 19% of ADH cases are not caused by a defect in either the LDLR, APOB or PCSK9 gene [
      • Marduel M.
      • Carrie A.
      • Sassolas A.
      • Devillers M.
      • Carreau V.
      • Di Filippo M.
      • et al.
      Molecular spectrum of autosomal dominant hypercholesterolemia in France.
      ]. Two other ADH loci have been localized on chromosomes 16q22.1 [
      • Marques-Pinheiro A.
      • Marduel M.
      • Rabes J.-P.
      • Devillers M.
      • Villeger L.
      • Allard D.
      • et al.
      A fourth locus for autosomal dominant hypercholesterolemia maps at 16q22.1.
      ] and 8q24.22 [
      • Cenarro A.
      • García-Otín A.-L.
      • Tejedor M.T.
      • Solanas M.
      • Jarauta E.
      • Junquera C.
      • et al.
      A presumptive new locus for autosomal dominant hypercholesterolemia mapping to 8q24.22.
      ], as well as mutations that segregate with the ADH disease in the apolipoprotein E (apoE) gene (APOE) [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ,
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ] and the signal transducing adaptor family member 1 gene (STAP1) [
      • Fouchier S.W.
      • Dallinga-Thie G.M.
      • Meijers J.C.M.
      • Zelcer N.
      • Kastelein J.J.P.
      • Defesche J.C.
      • et al.
      Mutations in STAP1 are associated with autosomal dominant hypercholesterolemia.
      ]. However recent functional studies showed that STAP1 does not alter plasma LDL-cholesterol in mice and humans [
      • Loaiza N.
      • Hartgers M.L.
      • Reeskamp L.F.
      • Balder J.-W.
      • Rimbert A.
      • Bazioti V.
      • et al.
      Taking one step back in familial hypercholesterolemia: STAP1 does not alter plasma LDL (Low-Density lipoprotein) cholesterol in mice and humans.
      ], and familial analyses showed no cosegregation with the disease for four predicted pathogenic variants [
      • Lamiquiz-Moneo I.
      • Restrepo-Córdoba M.A.
      • Mateo-Gallego R.
      • Bea A.M.
      • Del Pino Alberiche-Ruano M.
      • García-Pavía P.
      • et al.
      Predicted pathogenic mutations in STAP1 are not associated with clinically defined familial hypercholesterolemia.
      ], delisting STAP1 as an authentic ADH gene.
      Nine apoE variants (p.Glu21Lys, p.Leu46Pro, p.Gln99Lys-E4, p.Pro102Arg, p.Arg163Cys, p.Leu167del, apoE7-Suita, p.Arg269Gly, p.Leu270Glu) have been observed in single cases with hyperLDLemia (type IIa hyperlipoproteinemia), but the possible co-segregation with hypercholesterolemia in the families was not always analyzed [
      • Wardell M.R.
      • Rall S.C.
      • Schaefer E.J.
      • Kane J.P.
      • Weisgraber K.H.
      Two apolipoprotein E5 variants illustrate the importance of the position of additional positive charge on receptor-binding activity.
      ,
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ,
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ,
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ,
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ,
      • Tsuchiya S.
      • Yamanouchi Y.
      • Miyazaki R.
      • Yanagi H.
      • Yamakawa K.
      • Yuzawa K.
      • et al.
      Association of the apolipoprotein E4 allele with hypercholesterolemia in apparently healthy male adults in Tokyo.
      ,
      • Ruzicka V.
      • März W.
      • Russ A.
      • Fisher E.
      • Mondorf W.
      • Gross W.
      Characterization of the gene for apolipoprotein E5-Frankfurt (Gln81->Lys, Cys112->Arg) by polymerase chain reaction, restriction isotyping, and temperature gradient gel electrophoresis.
      ,
      • Kitahara M.
      • Shinomiya M.
      • Shirai K.
      • Saito Y.
      • Yoshida S.
      Frequency and role of apo E phenotype in familial hypercholesterolemia and non-familial hyperlipidemia in the Japanese.
      ,
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ,
      • van den Maagdenberg A.M.
      • Weng W.
      • de Bruijn I.H.
      • de Knijff P.
      • Funke H.
      • Smelt A.H.
      • et al.
      Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.
      ,
      • Faivre L.
      • Saugier-Veber P.
      • Pais de Barros J.-P.
      • Verges B.
      • Couret B.
      • Lorcerie B.
      • et al.
      Variable expressivity of the clinical and biochemical phenotype associated with the apolipoprotein E p.Leu149del mutation.
      ] (Table 1).
      Two variants in the APOE gene, p.Arg163Cys [
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ] and p.Leu167del [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ], were observed with a co-segregation with hyperLDLemia in the families. The p.Arg163Cys is carried by the mother, who is suffering from hypercholesterolemia with a LDL cholesterol of 270 mg/dL, and her son (LDL cholesterol 415 mg/dL) who is homozygote carrier [
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ]. The p.Leu167del variation was reported in two different families [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ]. A large French ADH family, with 14 affected members, was analyzed through whole genome linkage and whole exome sequencing and revealed that the p.Leu167del variation in the APOE gene is responsible of the ADH phenotype [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ]. Shortly after, an ADH family from Italian origin with two affected members, one with tendinous xanthomas, was analyzed through whole exome sequencing and also revealed the co-segregation of the p.Leu167del variant [
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ]. Kinetic studies of apo B-100-containing lipoproteins was performed in one p.Leu167del carrier of the French ADH family [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ]. LDL kinetic parameters were similar to those from FH patients (mutation in the LDLR gene) with an increased LDL pool, which was the consequence of both an increase in VLDL production rate and a decrease in LDL catabolism, and thus explaining the hyperLDLemia observed in the family [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ]. An explanation of the decreased LDL catabolism was given by the study of VLDL from p.Leu167del carriers showing a reduced expression of the LDLR gene when compared to VLDL from E3/E3 carriers [
      • Cenarro A.
      • Etxebarria A.
      • de Castro-Orós I.
      • Stef M.
      • Bea A.M.
      • Palacios L.
      • et al.
      The p.Leu167del Mutation in APOE Gene Causes Autosomal Dominant Hypercholesterolemia by Down-regulation of LDL Receptor Expression in Hepatocytes.
      ] (Fig. 1).
      The p.leu167del variant has been previously shown to segregate with familial combined hyperlipidemia (FCHL) in three families with a dominant transmission pattern [
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ]. The p.Leu167del variant has also been previously associated with familial splenomegaly and thrombocytopenia in two unrelated probands with mild hypertriglyceridemia that worsened after splenectomy [
      • Nguyen T.T.
      • Kruckeberg K.E.
      • O'Brien J.F.
      • Ji Z.-S.
      • Karnes P.S.
      • Crotty T.B.
      • et al.
      Familial splenomegaly: macrophage hypercatabolism of lipoproteins associated with apolipoprotein E mutation [apolipoprotein E (Δ149 leu)].
      ] and in one member from a family in which dyslipidemia segregated with the apoE p.leu167del variant [
      • Faivre L.
      • Saugier-Veber P.
      • Pais de Barros J.-P.
      • Verges B.
      • Couret B.
      • Lorcerie B.
      • et al.
      Variable expressivity of the clinical and biochemical phenotype associated with the apolipoprotein E p.Leu149del mutation.
      ]. Splenomegaly has been explained by an increased uptake of mutant p.Leu167del apoE-containing lipoproteins by macrophages [
      • Nguyen T.T.
      • Kruckeberg K.E.
      • O'Brien J.F.
      • Ji Z.-S.
      • Karnes P.S.
      • Crotty T.B.
      • et al.
      Familial splenomegaly: macrophage hypercatabolism of lipoproteins associated with apolipoprotein E mutation [apolipoprotein E (Δ149 leu)].
      ], but probably requires some other unknown defect to develop.
      Modelling analysis based on the NMR structure of the full-length apoE3 isoform was used for interpreting the effect of three variations identified in patients with type IIa hyperlipoproteinemia: p.Leu46Pro, p.Arg163Cys and p.Leu167del [
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ]. The p.Leu46Pro variant, located in the first of the four α-helix in the N-terminal domain, inserts a proline residue and thus was predicted to be destabilizing the α-helix. A previous analysis of the E4-p.Leu46Pro variant - which is associated with an increased risk of Alzheimer's disease (AD) (odds ratio (OR) 13.2) increasing the risk of the apoE4 alone by five times [
      • Argyri L.
      • Dafnis I.
      • Theodossiou T.A.
      • Gantz D.
      • Stratikos E.
      • Chroni A.
      Molecular basis for increased risk for late-onset Alzheimer disease due to the naturally occurring L28P mutation in apolipoprotein E4.
      ] - showed an affected stability and structure of the protein [
      • Corbo R.M.
      • Prévost M.
      • Raussens V.
      • Gambina G.
      • Moretto G.
      • Scacchi R.
      Structural and phylogenetic approaches to assess the significance of human Apolipoprotein E variation.
      ]. The p.Arg163Cys and p.Leu167del variants, in the receptor-binding domain (region 154–168) (Fig. 2), are thought to impair receptor-binding properties of the apoE protein (Fig. 1). Homology modeling of the human wild type apoE protein and of the deleted mutant was used for interpreting the effect of the p.Leu167del mutant [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ]. The p.Leu167del variation interrupts one α-helix in a group of four helices stabilized by a leucine zipper within the receptor-binding domain. Disruption of one helix in the group very probably alters the interaction with the three others. The electrostatic surface charges are altered in apoE p.Leu167del, that also likely influences interaction with lipids and affinity of apoE to its receptors [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ].
      Finally, among the 41 carriers of the apoE7-Suita reported, 27 presented normal lipid values, 6 were with hypertriglyceridemia, 5 were with isolated LDL increase, 2 presented mixed hyperlipidemia, and 1 was diagnosed with type III hyperlipoproteinemia (familial dysbetalipoproteinemia (FD)) (Table 2).
      Table 2Characteristics of ApoE7-Suita variant carriers.
      ApoE7 diagnosisAge (y.o.)SexFamilyApoE isoformsTotal-cholesterolTriglyceridesLDL-cholesterolHDL-cholesterolHyperlipidemiaReference
      IEF37MProbandE4/E73164829815hLDL[
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ]
      IEF32MBrotherE4/E73504729638hLDL[
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ]
      IEF57MProbandE3/E731112126238hLDL[
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ]
      IEF23FDaughterE2/E72068215838N[
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ]
      IEF74FProbandE3/E718814613631N[
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ]
      IEF40MProbandE4/E72715868026HTG[
      • Yamamura T.
      • Yamamoto A.
      • Sumiyoshi T.
      • Hiramori K.
      • Nishioeda Y.
      • Nambu S.
      New mutants of apolipoprotein E associated with atherosclerotic diseases but not to type III hyperlipoproteinemia.
      ]
      IEF54-ProbandE3/E7235144--N[
      • Tsuchiya S.
      • Yamanouchi Y.
      • Miyazaki R.
      • Yanagi H.
      • Yamakawa K.
      • Yuzawa K.
      • et al.
      Association of the apolipoprotein E4 allele with hypercholesterolemia in apparently healthy male adults in Tokyo.
      ]
      IEF + SEQ55MProbandE3/E7205483-49HTG[
      • Maeda H.
      • Nakamura H.
      • Kobori S.
      • Okada M.
      • Mori H.
      • Niki H.
      • et al.
      Identification of human apolipoprotein E variant gene: apolipoprotein E7 (Glu244,245–--Lys244,245).
      ]
      IEF--ProbandE3/E7----Type IIa[
      • Kitahara M.
      • Shinomiya M.
      • Shirai K.
      • Saito Y.
      • Yoshida S.
      Frequency and role of apo E phenotype in familial hypercholesterolemia and non-familial hyperlipidemia in the Japanese.
      ]
      IEF--ProbandE4/E7----Type III[
      • Kitahara M.
      • Shinomiya M.
      • Shirai K.
      • Saito Y.
      • Yoshida S.
      Frequency and role of apo E phenotype in familial hypercholesterolemia and non-familial hyperlipidemia in the Japanese.
      ]
      IEF--ProbandE4/E7----Type IV[
      • Kitahara M.
      • Shinomiya M.
      • Shirai K.
      • Saito Y.
      • Yoshida S.
      Frequency and role of apo E phenotype in familial hypercholesterolemia and non-familial hyperlipidemia in the Japanese.
      ]
      IEF + PCR85FProbandE3/E7184878680N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR67MProbandE3/E71779912235N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR60MProbandE4/E726518019137N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR55MProbandE3/E720116413732N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR55MProbandE3/E725919518832N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR54FProbandE3/E72027312266N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR52FProbandE3/E72039211470N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR51MProbandE3/E71837812443N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR50MProbandE3/E730416021755hLDL[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR46FProbandE3/E718911613233N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR45MProbandE3/E720920610959Mixed[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR32MProbandE3/E725219917735N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR26MProbandE3/E720718312446N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR22FProbandE3/E71864910373N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR21FProbandE3/E72578416872N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR17MProbandE3/E72059013552N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR17FProbandE4/E72047812960N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR17FProbandE3/E71251824761N[
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ]
      IEF + PCR66MProbandE3/E726815718236N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR60MProbandE3/E731016722846N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR44MProbandE3/E726350711450HTG[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR48MProbandE3/E71273383933HTG[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR55MProbandE3/E71933266641HTG[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR47MProbandE3/E728137672Mixed[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR48FProbandE3/E71651795646N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR25MProbandE3/E71929912640N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR22FProbandE3/E7176938756N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR22FProbandE3/E7157656075N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR10MProbandE3/E7152996264N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      IEF + PCR11MProbandE4/E7131666330N[
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ]
      Lipid parameters are given in mg/dL. Type IIa, IIa, III, IV clinical phenotypes were distinguished according to WHO criteria. Type III hyperlipidemia was recognized by the presence of a mid-band larger than the LDL band on electrophoresis [
      • Kitahara M.
      • Shinomiya M.
      • Shirai K.
      • Saito Y.
      • Yoshida S.
      Frequency and role of apo E phenotype in familial hypercholesterolemia and non-familial hyperlipidemia in the Japanese.
      ].
      IEF: isoelectric focusing. SEQ: Sequencing of the p.Glu262Lys/p.Glu263Lys variant. PCR: PCR‐mediated site‐directed mutagenesis of the p.Glu262Lys/p.Glu263Lys variant.
      hLDL: hyperLDLemia. HC: primary hypercholesterolaemia. HTG; hypertriglyceridemia. N: normolipidemic.

      3. ApoE and familial combined hyperlipidemia (FCHL)

      Familial combined hyperlipidemia (FCHL) is a common disorder of lipid metabolism which leads to elevated levels of VLDL, LDL, or both in plasma, leading to a mixed hyperlipidemia with both high total-cholesterol and triglycerides levels. FCHL occurs in up to 1–3% of the general population and may account for one third to one half of familial causes of early coronary heart disease [
      • Bello-Chavolla O.Y.
      • Kuri-García A.
      • Ríos-Ríos M.
      • Vargas-Vázquez A.
      • Cortés-Arroyo J.E.
      • Tapia-González G.
      • et al.
      Familial combined hyperlipidemia: current knowledge, perspectives, and controversies.
      ]. The phenotype of FCHL is highly variable among family members, depending on genetic and environmental factors, and may present as mixed hyperlipidemia, isolated hypercholesterolemia, hypertriglyceridemia, or as a normal serum lipid profile in combination with abnormally elevated levels of apolipoprotein B. The presence of small dense LDL particles has also been associated with FCHL. Small dense LDL particles are generated when triglyceride-rich VLDL particles are abundant. VLDL particles can exchange their triglyceride molecules for cholesteryl esters from LDL particles which results in cholesterol-depleted LDL particles [
      • Brouwers M.C.G.J.
      • van Greevenbroek M.M.J.
      • Stehouwer C.D.A.
      • de Graaf J.
      • Stalenhoef A.F.H.
      The genetics of familial combined hyperlipidaemia.
      ]. In the circulation, LDL particles are substrate for endothelial-bound lipases which leads to the formation of smaller and more dense particles [
      • Packard C.J.
      • Shepherd J.
      Lipoprotein heterogeneity and apolipoprotein B metabolism.
      ]. Affected individuals may have variable degrees of elevated total cholesterol, triglycerides, or LDL cholesterol and are at high risk for premature atherosclerotic cardiovascular disease.
      FCHL is a genetically complex disorder with reduced penetrance. Most cases of FCHL are considered polygenic with the interaction of multiple susceptibility factors. Many of the genes contributing to FCHL are unknown: susceptibility loci have been reported at 1q21-23, 11p14.1 and 16q22–24.1, and a consistent association with the chromosome 11 loci has been shown [
      • Bello-Chavolla O.Y.
      • Kuri-García A.
      • Ríos-Ríos M.
      • Vargas-Vázquez A.
      • Cortés-Arroyo J.E.
      • Tapia-González G.
      • et al.
      Familial combined hyperlipidemia: current knowledge, perspectives, and controversies.
      ]. This locus contains several candidate genes such as the upstream transcription factor 1 gene (USF1) which encodes a transcription factor that regulates numerous genes of the lipoprotein metabolism including APOE. However, several genes have already been described in FCHL and have been associated with three major metabolic pathways: adipose tissue dysfunction, hepatic fat accumulation and overproduction, disturbed metabolism and delayed clearance of apolipoprotein B-containing particles [
      • Brouwers M.C.G.J.
      • van Greevenbroek M.M.J.
      • Stehouwer C.D.A.
      • de Graaf J.
      • Stalenhoef A.F.H.
      The genetics of familial combined hyperlipidaemia.
      ]. ApoE serves as the ligand for the clearance of triglyceride-rich lipoproteins and as a co-factor for lipoprotein lipase (LPL) responsible for the hydrolysis of triglycerides in VLDL driving the formation of IDL and LDL. Thus, a variation of either the structure or the function of apoE could have an impact on the metabolism and clearance of triglyceride-rich lipoproteins and the development of FCHL [
      • Brouwers M.C.G.J.
      • van Greevenbroek M.M.J.
      • Stehouwer C.D.A.
      • de Graaf J.
      • Stalenhoef A.F.H.
      The genetics of familial combined hyperlipidaemia.
      ]. Eight variants in the APOE gene have been reported with either FCHL or mixed hyperlipidemia (Table 1). Three variants - p.Arg154Ser, p.Leu167del, p.Glu230Lys – were reported in families with a dominant transmission of a mixed hyperlipidaemia phenotype defining FCHL [
      • Feussner G.
      • Scharnagl H.
      • Scherbaum C.
      • Acar J.
      • Dobmeyer J.
      • Lohrmann J.
      • et al.
      Apolipoprotein E5 (Glu212-->Lys): increased binding to cell surface proteoglycans but decreased uptake and lysosomal degradation in cultured fibroblasts.
      ,
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ]. The two first variants are in the receptor-binding domain, while the p.Glu230Lys is in the hinge domain (Fig. 2). Receptor-binding studies have shown that p.Arg154Ser apoE mutant had only 41% of the apoE3 receptor binding capacity. Moreover, lipoprotein turnover studies showed a significantly reduced catabolic rate of VLDL particles from patient carrying the p.Arg154Ser variant [
      • Wardell M.R.
      • Brennan S.O.
      • Janus E.D.
      • Fraser R.
      • Carrell R.W.
      Apolipoprotein E2-Christchurch (136 Arg–--Ser). New variant of human apolipoprotein E in a patient with type III hyperlipoproteinemia.
      ] (Fig. 1). When associated with apoE2, p.Glu230Lys modifies the binding preference of apoE-containing particles from lipoprotein receptors to proteoglycans reducing the uptake and degradation of these particles. This could explain the increased of triglycerides in p.Glu230Lys carriers [
      • Feussner G.
      • Scharnagl H.
      • Scherbaum C.
      • Acar J.
      • Dobmeyer J.
      • Lohrmann J.
      • et al.
      Apolipoprotein E5 (Glu212-->Lys): increased binding to cell surface proteoglycans but decreased uptake and lysosomal degradation in cultured fibroblasts.
      ] (Fig. 1). Five variants - p.Gly145Asp-E2, p.Arg235Trp, p.Arg242Gln, p.Val254Glu-E2, apoE7 - were reported in single cases presenting with a mixed hyperlipidaemia phenotype [
      • Matsunaga A.
      • Sasaki J.
      • Moriyama K.
      • Arakawa F.
      • Takada Y.
      • Nishi K.
      • et al.
      Population frequency of apolipoprotein E5 (Glu3-->Lys) and E7 (Glu244-->Lys, Glu245-->Lys) variants in western Japan.
      ,
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ,
      • Yanagi K.
      • Yamashita S.
      • Hiraoka H.
      • Ishigami M.
      • Kihara S.
      • Hirano K.
      • et al.
      Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita).
      ,
      • van den Maagdenberg A.M.
      • Weng W.
      • de Bruijn I.H.
      • de Knijff P.
      • Funke H.
      • Smelt A.H.
      • et al.
      Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.
      ,
      • Moriyama K.
      • Sasaki J.
      • Takada Y.
      • Arakawa F.
      • Matsunaga A.
      • Ito Y.
      • et al.
      Characterization of a novel variant of apolipoprotein E, E2 Fukuoka (Arg-224--> Gln) in a hyperlipidemic patient with xanthomatosis.
      ]. However, without notion of familial segregation, it is not possible to confirm the involvement of these variants in the pathogenesis of FCHL. Furthermore, without information on the level of VLDL-remnants (IDL), it is also not possible to validate the participation of these variants in the genetic heterogeneity of type III hyperlipidaemia (familial dysbetalipoproteinemia (FD)).

      4. ApoE and familial dysbetalipoproteinemia (FD)

      Familial dysbetalipoproteinemia (FD), also called type III hyperlipoproteinemia, is an atherogenic disorder characterized by a mixed hyperlipidaemia, due to accumulation of VLDL remnants and IDL, similar to the FHCL phenotype. As for FHCL, the FD phenotype is highly variable. The diagnosis of FD can easily be performed by lipoprotein electrophoresis using either agarose or polyacrylamide gel disc electrophoresis or by gel-permeation high-performance liquid chromatography (GP-HPLC). FD is diagnosed based upon the presence of broad beta pattern and increase of chylomicron and VLDL remnants. FD is due to dysfunctional genetic variants of apolipoprotein E with the homozygous E2/E2 in most of the cases. However, only 1–4% of the E2/E2 carriers will developpe FD [
      • Rall S.C.
      • Weisgraber K.H.
      • Innerarity T.L.
      • Bersot T.P.
      • Mahley R.W.
      • Blum C.B.
      Identification of a new structural variant of human apolipoprotein E, E2(Lys146 leads to Gln), in a type III hyperlipoproteinemic subject with the E3/2 phenotype.
      ] indicating that additional factors are necessary for manifestation of FD. In contrast to lipoprotein analysis, the identification of the apoE isoform is easily obtained by isoelectric focusing, PCR‐mediated site‐directed mutagenesis, or direct gene sequencing.
      Thirty-one variants in the APOE gene have been reported in hyperlipidemic patients presenting FD diagnosed by the presence of a broad β migrating band on the electrophoresis separation of lipoproteins (Table 1). The first apoE mutant in type III hyperlipoproteinemia (FD) reported is the ApoE3-Leiden variant characterized by an in-frame repeat of 21 nucleotides in exon 4 leading to a 7 amino-acid duplication, p.Glu139_Gly145dup, localized 9 residues before the receptor-binding domain (154–168) [
      • Havekes L.
      • de Wit E.
      • Leuven J.G.
      • Klasen E.
      • Utermann G.
      • Weber W.
      • et al.
      Apolipoprotein E3-Leiden. A new variant of human apolipoprotein E associated with familial type III hyperlipoproteinemia.
      ]. The seven-amino acid insert introduces one extra negatively charged glutamyl residue when compared with the common apoE4 variant and thus leads to a focusing on the apoE3 position on isoelectric focusing gels [
      • Havekes L.
      • de Wit E.
      • Leuven J.G.
      • Klasen E.
      • Utermann G.
      • Weber W.
      • et al.
      Apolipoprotein E3-Leiden. A new variant of human apolipoprotein E associated with familial type III hyperlipoproteinemia.
      ]. ApoE3-Leiden is defective in binding to the LDL receptor. The p.Arg154Ser variant, APOE-Christchurch, has been identified in hyperlipidemic patients presenting FCHL, FD or primary hypertriglyceridemia (HTG) illustrating the variability of the phenotype and the difficulty of clinical diagnosis [
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ,
      • Wardell M.R.
      • Brennan S.O.
      • Janus E.D.
      • Fraser R.
      • Carrell R.W.
      Apolipoprotein E2-Christchurch (136 Arg–--Ser). New variant of human apolipoprotein E in a patient with type III hyperlipoproteinemia.
      ,
      • Pocovi M.
      • Cenarro A.
      • Civeira F.
      • Myers R.H.
      • Casao E.
      • Esteban M.
      • et al.
      Incomplete dominance of type III hyperlipoproteinemia is associated with the rare apolipoprotein E2 (Arg136-->Ser) variant in multigenerational pedigree studies.
      ,
      • Civeira F.
      • Pocoví M.
      • Cenarro A.
      • Casao E.
      • Vilella E.
      • Joven J.
      • et al.
      Apo E variants in patients with type III hyperlipoproteinemia.
      ,
      • Lamiquiz-Moneo I.
      • Blanco-Torrecilla C.
      • Bea A.M.
      • Mateo-Gallego R.
      • Pérez-Calahorra S.
      • Baila-Rueda L.
      • et al.
      Frequency of rare mutations and common genetic variations in severe hypertriglyceridemia in the general population of Spain.
      ]. The p.Arg160Cys-E4 variant has been shown to segregate with the FD phenotype in a 6-member family on the dominant mode [
      • Rall S.C.
      • Newhouse Y.M.
      • Clarke H.R.
      • Weisgraber K.H.
      • McCarthy B.J.
      • Mahley R.W.
      • et al.
      Type III hyperlipoproteinemia associated with apolipoprotein E phenotype E3/3. Structure and genetics of an apolipoprotein E3 variant.
      ]. Functional analysis of this variant either on the E3 or E4 isoform showed a significantly reduced receptor- and heparin-binding activity on human fibroblasts indicating that the cysteine at residue 160, and not the E4 arginine at residue 130, is responsible for the decreased receptor-binding activity of the variant [
      • Horie Y.
      • Fazio S.
      • Westerlund J.R.
      • Weisgraber K.H.
      • Rall S.C.
      The functional characteristics of a human apolipoprotein E variant (cysteine at residue 142) may explain its association with dominant expression of type III hyperlipoproteinemia.
      ]. The apoE1 p.Lys164Glu variant has also been shown to segregate with the FD phenotype in a 12-member family on the dominant mode [
      • Mann W.A.
      • Gregg R.E.
      • Sprecher D.L.
      • Brewer H.B.
      Apolipoprotein E-1Harrisburg: a new variant of apolipoprotein E dominantly associated with type III hyperlipoproteinemia.
      ] and characterized with a higher production rate, and a reduced catabolism due to its reduced affinity for the LDL receptor and for heparin [
      • Moriyama K.
      • Sasaki J.
      • Matsunaga A.
      • Arakawa F.
      • Takada Y.
      • Araki K.
      • et al.
      Apolipoprotein E1 Lys-146–--Glu with type III hyperlipoproteinemia.
      ,
      • Mann W.A.
      • Lohse P.
      • Gregg R.E.
      • Ronan R.
      • Hoeg J.M.
      • Zech L.A.
      • et al.
      Dominant expression of type III hyperlipoproteinemia. Pathophysiological insights derived from the structural and kinetic characteristics of ApoE-1 (Lys146-->Glu).
      ]. The p.Lys164Gln, associated with the E2 isoform, has defective binding activity for the lipoprotein receptors [
      • Rall S.C.
      • Weisgraber K.H.
      • Innerarity T.L.
      • Bersot T.P.
      • Mahley R.W.
      • Blum C.B.
      Identification of a new structural variant of human apolipoprotein E, E2(Lys146 leads to Gln), in a type III hyperlipoproteinemic subject with the E3/2 phenotype.
      ]. Moreover, 4 variants - p.Trp5*, p.Arg145Cys, p.Arg154Ser, p.Ala227Glyfs*20 [
      • Pocovi M.
      • Cenarro A.
      • Civeira F.
      • Myers R.H.
      • Casao E.
      • Esteban M.
      • et al.
      Incomplete dominance of type III hyperlipoproteinemia is associated with the rare apolipoprotein E2 (Arg136-->Ser) variant in multigenerational pedigree studies.
      ,
      • Leren T.P.
      • Strøm T.B.
      • Berge K.E.
      Variable phenotypic expression of nonsense mutation p.Thr5* in the APOE gene.
      ,
      • de Villiers W.J.
      • van der Westhuyzen D.R.
      • Coetzee G.A.
      • Henderson H.E.
      • Marais A.D.
      The apolipoprotein E2 (Arg145Cys) mutation causes autosomal dominant type III hyperlipoproteinemia with incomplete penetrance.
      ,
      • Feussner G.
      • Dobmeyer J.
      • Gröne H.J.
      • Lohmer S.
      • Wohlfeil S.A.
      10-bp deletion in the apolipoprotein epsilon gene causing apolipoprotein E deficiency and severe type III hyperlipoproteinemia.
      ] - were shown to be inherited on the autosomal dominant mode with reduced penetrance, adding complexity to the molecular diagnosis.

      5. ApoE and lipoprotein glomerulopathy (LPG)

      Lipoprotein glomerulopathy (LPG) is a renal disease in which lipid deposition is limited to the kidney and is believed to cause glomerulosclerosis. This disease is characterized by glomerular lipoprotein thrombi and clinically by proteinuria and type III hyperlipoproteinemia with apoE abnormality [
      • Saito T.
      • Matsunaga A.
      • Fukunaga M.
      • Nagahama K.
      • Hara S.
      • Muso E.
      Apolipoprotein E-related glomerular disorders.
      ,
      • Yang M.
      • Weng Q.
      • Pan X.
      • Hussain H.M.J.
      • Yu S.
      • Xu J.
      • et al.
      Clinical and genetic analysis of lipoprotein glomerulopathy patients caused by APOE mutations.
      ]. The elevated plasma apoE concentration caused by reduced receptor-binding activity is an important determinant for the development of LPG. However, hyperlipidaemia in LPG is often milder than in type III hyperlipoproteinemia, or not even recognized in some cases of LPG. Seventeen variants in the APOE gene have been reported in lipoprotein glomerulopathy (LPG) (Table 1). Several variants were reported in single cases with various disease expression from the p.Arg132Cys in a normolipidemic patient with normal levels of apoE [
      • Hagiwara M.
      • Yamagata K.
      • Matsunaga T.
      • Arakawa Y.
      • Usui J.
      • Shimizu Y.
      • et al.
      A novel apolipoprotein E mutation, ApoE Tsukuba (Arg 114 Cys), in lipoprotein glomerulopathy.
      ] to the p.Ser215Cys-E2/E2 in a type III hyperlipidaemic patient [
      • Kato T.
      • Ushiogi Y.
      • Yokoyama H.
      • Hara S.
      • Matsunaga A.
      • Muso E.
      • et al.
      A case of apolipoprotein E Toyonaka and homozygous apolipoprotein E2/2 showing non-immune membranous nephropathy-like glomerular lesions with foamy changes.
      ]. Four variants - p.Arg43Cys, p.Lys161_Arg165del, p.Arg168Cys, p.Arg168Pro - were reported in families with a dominant transmission and a reduced penetrance [
      • Matsunaga A.
      • Sasaki J.
      • Komatsu T.
      • Kanatsu K.
      • Tsuji E.
      • Moriyama K.
      • et al.
      A novel apolipoprotein E mutation, E2 (Arg25Cys), in lipoprotein glomerulopathy.
      ,
      • Xie W.
      • Xie Y.
      • Lin Z.
      • Xu X.
      • Zhang Y.
      A novel apolipoprotein E mutation caused by a five amino acid deletion in a Chinese family with lipoprotein glomerulopathy: a case report.
      ,
      • Ku M.
      • Tao C.
      • Zhou A.-A.
      • Cheng Y.
      • Wan Q.-J.
      A novel apolipoprotein E mutation (p.Arg150Cys) in a Chinese patient with lipoprotein glomerulopathy.
      ,
      • Luo B.
      • Huang F.
      • Liu Q.
      • Li X.
      • Chen W.
      • Zhou S.-F.
      • et al.
      Identification of apolipoprotein E Guangzhou (arginine 150 proline), a new variant associated with lipoprotein glomerulopathy.
      ].

      6. Overlaps between ADH, FCHL, FD and LPG

      Mutations in the LDLR gene were reported in patients with a clinical diagnosis of FCHL [
      • Civeira F.
      • Jarauta E.
      • Cenarro A.
      • García-Otín A.L.
      • Tejedor D.
      • Zambón D.
      • et al.
      Frequency of low-density lipoprotein receptor gene mutations in patients with a clinical diagnosis of familial combined hyperlipidemia in a clinical setting.
      ]. A study conducted on 143 unrelated FCHL patients showed that 19.6% were carriers of LDLR mutations. Some of these mutations have been previously identified as the cause of ADH indicating that patients with ADH presenting with hypertriglyceridemia may be misdiagnosed with FCHL [
      • Civeira F.
      • Jarauta E.
      • Cenarro A.
      • García-Otín A.L.
      • Tejedor D.
      • Zambón D.
      • et al.
      Frequency of low-density lipoprotein receptor gene mutations in patients with a clinical diagnosis of familial combined hyperlipidemia in a clinical setting.
      ]. Interestingly, APOE variants were also identified in patients diagnosed with FCHL [
      • Civeira F.
      • Jarauta E.
      • Cenarro A.
      • García-Otín A.L.
      • Tejedor D.
      • Zambón D.
      • et al.
      Frequency of low-density lipoprotein receptor gene mutations in patients with a clinical diagnosis of familial combined hyperlipidemia in a clinical setting.
      ] and the same APOE variant can be reported with both FCHL and ADH. Rare APOE mutations are responsible for 3.5% of FCHL cases in a Spanish population [
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ] out of which 1.4% were carriers of the p.Leu167del variant [
      • Solanas-Barca M.
      • de Castro-Orós I.
      • Mateo-Gallego R.
      • Cofán M.
      • Plana N.
      • Puzo J.
      • et al.
      Apolipoprotein E gene mutations in subjects with mixed hyperlipidemia and a clinical diagnosis of familial combined hyperlipidemia.
      ] already identified as the causative mutations of ADH in two different families [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ]. The APOE p.Arg163Cys variant was found, in association with the E2 isoform, in a single case with FD [
      • Emi M.
      • Wu L.L.
      • Robertson M.A.
      • Myers R.L.
      • Hegele R.A.
      • Williams R.R.
      • et al.
      Genotyping and sequence analysis of apolipoprotein E isoforms.
      ], and in a family with ADH [
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ]. The association of the p.Arg163Cys variant with the E2 common polymorphism may amplify effects contributing to the triglyceride elevation that differentiate FD from ADH. Moreover, the overlapping clinical presentation of FCHL and ADH exists [
      • Civeira F.
      • Jarauta E.
      • Cenarro A.
      • García-Otín A.L.
      • Tejedor D.
      • Zambón D.
      • et al.
      Frequency of low-density lipoprotein receptor gene mutations in patients with a clinical diagnosis of familial combined hyperlipidemia in a clinical setting.
      ], hypertriglyceridemia can sometimes be observed in ADH subjects, mainly because of the many common genetic, metabolic and environmental factors contributing to triglyceride elevation, or perhaps epigenetic and other non-mendelian interacting effects. Variants in the LDLR or APOE gene may amplify the effect of these factors, and thus, according to the number or the nature of these factors, could be associated with an overlapping phenotype between FCHL, ADH and sometimes FD when the subject is E2/E2. The genotyping of APOE and the exclusion of LDLR and APOE variants in patients with combined dyslipidemia could be very informative for the differential diagnosis of lipid disorders. The current diagnostic criteria for ADH, excluding all patients presenting high triglyceride levels, could be responsible for an underdiagnosis and hence an undertreatment of the disease. Furthermore, many glomerular disorders caused by abnormalities in apoE-containing lipoproteins have been identified. Of these disorders, lipoprotein glomerulopathy and apoE2 homozygote glomerulopathy have been characterized and differentiated histologically [
      • Saito T.
      • Matsunaga A.
      • Fukunaga M.
      • Nagahama K.
      • Hara S.
      • Muso E.
      Apolipoprotein E-related glomerular disorders.
      ]. However, both disorders present with a lipid profile similar to FD [
      • Saito T.
      • Matsunaga A.
      • Fukunaga M.
      • Nagahama K.
      • Hara S.
      • Muso E.
      Apolipoprotein E-related glomerular disorders.
      ]. In fact, apoE homozygosity is considered responsible for FD, but only 10 cases of apoE2 homozygote glomerulopathy were reported worldwide. The presence of other factors seems necessary to trigger the disease. LPG was first identified as a glomerular disease associated with type III hypercholesterolemia. Genetic studies identified numerous heterozygotes APOE variants associated with LPG, most of them are located within the receptor-binding domain. Whilst, it was previously perceived that FD observed in the patients is responsible for the LPG phenotype, current studies claim that the abnormal lipid-free apoE structure and aggregation caused by APOE variants are the cause behind the development of LPG. Pathological studies have shown that, in contrast with homozygote E2 glomerulopathy, treatment with fibrates is effective for the management of hypertriglyceridemia in LPG, but not homozygote E2 glomerulopathy, and could prevent the glomerular damage [
      • Arai T.
      • Yamashita S.
      • Yamane M.
      • Manabe N.
      • Matsuzaki T.
      • Kiriyama K.
      • et al.
      Disappearance of intraglomerular lipoprotein thrombi and marked improvement of nephrotic syndrome by bezafibrate treatment in a patient with lipoprotein glomerulopathy.
      ,
      • Hu Z.
      • Huang S.
      • Wu Y.
      • Liu Y.
      • Liu X.
      • Su D.
      • et al.
      Hereditary features, treatment, and prognosis of the lipoprotein glomerulopathy in patients with the APOE Kyoto mutation.
      ]. Thus, both genotyping and sequencing of APOE could be very useful in patients with a FD-like phenotype in order to set the diagnosis, the prevention and the treatment of the glomerular diseases and their consequences on renal dysfunction.

      7. Conclusion

      Common APOE variants are associated with variations in lipid and lipoprotein levels alongside with other common genetic and environmental factors influencing the clinical presentation of lipid disorders associated with rare APOE variants.The identification of the APOE p.Leu167del variant as the causative molecular element in two different ADH families [
      • Marduel M.
      • Ouguerram K.
      • Serre V.
      • Bonnefont-Rousselot D.
      • Marques-Pinheiro A.
      • Erik Berge K.
      • et al.
      Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.
      ,
      • Awan Z.
      • Choi H.Y.
      • Stitziel N.
      • Ruel I.
      • Bamimore M.A.
      • Husa R.
      • et al.
      APOE p.Leu167del mutation in familial hypercholesterolemia.
      ], paved the way to consider APOE as a candidate gene for ADH. Recent works showed that causal variants in APOE are not an insignificant cause of ADH with a frequency of 1.3% of affected patients in a French cohort [
      • Wintjens R.
      • Bozon D.
      • Belabbas K.
      • MBou F.
      • Girardet J.-P.
      • Tounian P.
      • et al.
      Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France.
      ] and 3.1% in a Spanish cohort [
      • Cenarro A.
      • Etxebarria A.
      • de Castro-Orós I.
      • Stef M.
      • Bea A.M.
      • Palacios L.
      • et al.
      The p.Leu167del Mutation in APOE Gene Causes Autosomal Dominant Hypercholesterolemia by Down-regulation of LDL Receptor Expression in Hepatocytes.
      ]. On the contrary, APOE causative variants are not a common cause of hypercholesterolemia in a Norwegian population with a frequency of 0.2% [
      • Leren T.P.
      • Strøm T.B.
      • Berge K.E.
      Variable phenotypic expression of nonsense mutation p.Thr5* in the APOE gene.
      ]. Altogether, these results show that screening of the APOE gene is warranted in the setting of molecular diagnosis of ADH along with the LDLR, APOB, and PCSK9 genes. Which will be routinely possible with the progressive use of next generation sequencing (NGS). The molecular diagnostics is warranted to allow the constitution of homogeneous cohorts of patients, and to understand the natural history and the evolution with age of lipid diseases associated with the different variants of apoE. This will also make it possible, as has been widely reported for FH, to set up cascade screening allowing the diagnosis of relatives at risk and their early treatment. Finally, for the patient itself, it has been shown that knowledge of the mutation leads to better adherence to treatment. More studies are needed to determine the spectrum of implication of APOE in various lipid disorders, notably ADH, in order to improve clinical and genetic diagnosis, prognosis and patient care management.

      Financial support

      This work was supported by grants from Leducq Foundation ( FLQ # 13CVD03 ), The national project CHOPIN (CHolesterol Personalized Innovation) granted by the National Research Agency ( ANR-16-RHUS-0007 ), INSERM (Institut National de la Santé et de la Recherche Médicale) , Conseil de la recherche of Saint-Joseph University of Beirut , and CEDRE program .
      YAK is supported by a grant from Ministère de l’Education Nationale et de la Technologie (France) , a grant from Nouvelle Société Francophone de l’Athérosclérose (France) , and a grant from Lebanese National Council for Scientifc Research (CNRS-L) .

      Author contributions

      All authors contributed to the writing of this review.
      All authors have given final approval of the manuscript, and agree to be accountable for the work.

      Declaration of competing interest

      The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

      References

        • Marais A.D.
        Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease.
        Pathology. 2019; 51: 165-176https://doi.org/10.1016/j.pathol.2018.11.002
        • Bonaterra-Pastra A.
        • Fernández-de-Retana S.
        • Rivas-Urbina A.
        • Puig N.
        • Benítez S.
        • Pancorbo O.
        • et al.
        Comparison of plasma lipoprotein composition and function in cerebral Amyloid Angiopathy and Alzheimer's disease.
        Biomedicines. 2021; 9https://doi.org/10.3390/biomedicines9010072
        • Croyal M.
        • Blanchard V.
        • Ouguerram K.
        • Chétiveaux M.
        • Cabioch L.
        • Moyon T.
        • et al.
        VLDL (Very-Low-Density lipoprotein)-apo E (apolipoprotein E) may influence lp(a) (lipoprotein [a]) synthesis or assembly.
        Arterioscler. Thromb. Vasc. Biol. 2020; 40: 819-829https://doi.org/10.1161/ATVBAHA.119.313877
        • Sacks F.M.
        The crucial roles of apolipoproteins E and C-III in apoB lipoprotein metabolism in normolipidemia and hypertriglyceridemia.
        Curr. Opin. Lipidol. 2015; 26: 56-63https://doi.org/10.1097/MOL.0000000000000146
        • Huang Y.
        • Mahley R.W.
        • Apolipoprotein E.
        Structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases.
        Neurobiol. Dis. 2014; 72: 3-12https://doi.org/10.1016/j.nbd.2014.08.025
        • Brouwers M.C.G.J.
        • van Greevenbroek M.M.J.
        • Stehouwer C.D.A.
        • de Graaf J.
        • Stalenhoef A.F.H.
        The genetics of familial combined hyperlipidaemia.
        Nat. Rev. Endocrinol. 2012; 8: 352-362https://doi.org/10.1038/nrendo.2012.15
        • Packard C.J.
        • Shepherd J.
        Lipoprotein heterogeneity and apolipoprotein B metabolism.
        Arterioscler. Thromb. Vasc. Biol. 1997; 17: 3542-3556https://doi.org/10.1161/01.atv.17.12.3542
        • Hara M.
        • Iso-O N.
        • Satoh H.
        • Noto H.
        • Togo M.
        • Ishibashi S.
        • et al.
        Differential effects of apolipoprotein E isoforms on lipolysis of very low-density lipoprotein triglycerides.
        Metabolism. 2006; 55: 1129-1134https://doi.org/10.1016/j.metabol.2006.04.009