Association of the apolipoprotein E4 allele with hypercholesterolemia in apparently healthy male adults in Tokyo

Genetic and molecular architecture of familial hypercholesterolemia

Atherosclerotic cardiovascular disease is the leading cause of death globally. Despite its important risk of premature atherosclerosis and cardiovascular disease, familial hypercholesterolemia (FH) is still largely underdiagnosed worldwide. It is one of the most frequently inherited diseases due to mutations, for autosomal dominant forms, in either of the LDLR, APOB, and PCSK9 genes or possibly a few mutations in the APOE gene and, for the rare autosomal forms, in the LDLRAP1 gene. The discovery of the genes implicated in the disease has largely helped to improve the diagnosis and treatment of FH from the LDLR by Brown and Goldstein, as well as the introduction of statins, to PCSK9 discovery in FH by Abifadel et al., and the very rapid availability of PCSK9 inhibitors. In the last two decades, major progress has been made in clinical and genetic diagnostic tools and the therapeutic arsenal against FH. Improving prevention, diagnosis, and treatment and making them more accessible to all patients will help reduce the lifelong burden of the disease.

APOE gene variants in primary dyslipidemia

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.

The response to lovastatin treatment in patients with heterozygous familial hypercholesterolemia is modulated by apolipoprotein E polymorphism

In a retrospective study, we examined the influence of apolipoprotein (apo) E polymorphism and gender on the response to treatment with 80 mg/d lovastatin in a homogeneous population of patients with familial hypercholesterolemia (FH), most of whom were carriers of the 10-kb deletion of the low-density lipoprotein (LDL) receptor gene. Apo E phenotype distribution among the 189 FH patients was not different from that of a normal population sample. The total and LDL cholesterol (LDL-C) response to lovastatin in the overall group (men and women) was significantly lower in the E4 subset compared with E2 and E3 subsets. This finding is in agreement with trends observed in previous reports. On the other hand, the response of LDL-C to lovastatin was significantly lower in E4 men than in E4 women, whereas the high-density lipoprotein cholesterol (HDL-C) concentration in the E4 group increased significantly more in men than in women, suggesting a role of gender in modulating the response to lovastatin. Hence, apo E polymorphism influenced LDL-C (and HDL-C) response to lovastatin in men, but not in women, revealing the existence of a gene-by-gender interaction. These findings were independent of the nature of the LDL receptor defect. We conclude that male FH patients carrying the epsilon 4 allele respond less efficiently to lovastatin than men carrying the epsilon 3 or epsilon 2 allele or women of any apo E phenotype with respect to decreasing total cholesterol and LDL-C levels, but respond more efficiently with respect to increasing HDL-C levels. The full practical implication of these findings remains to be explored.

Association of hypercholesterolemia and apolipoprotein E4 in school children

To investigate the association of apolipoprotein (APO) E4 and hypercholesterolemia in children, we studied the APOE phenotypes of 51 school-age children with hypercholesterolemia and of 51 age, sex and obesity index-matched controls with normocholesterolemia by two-dimensional gel electrophoresis APOE4 was present in 21 of 51 hypercholesterolemic children (41.2%), and in nine of 51 control subjects (17.6%). The difference was significant (p less than 0.01). This finding indicates that APOE4 is associated with hypercholesterolemia in children.

The influence of apolipoprotein E phenotype on the response to lovastatin therapy in patients with heterozygous familial hypercholesterolemia

Apolipoprotein E (apo E) phenotypes have been previously shown to influence plasma lipoprotein concentrations in normal populations and to affect the response to some lipid lowering drugs. The purpose of the present study was to determine if variations in the apo E phenotype also affect basal lipoprotein concentrations in patients with heterozygous familial hypercholesterolemia (FH) and if the apo E phenotype influenced their subsequent response to lovastatin. Apo E phenotypes were determined on plasma from 134 FH patients. The relative frequencies of the epsilon 2, epsilon 3, and epsilon 4 alleles were .090, .772, and .138, respectively. Plasma triglycerides were found to be 34% higher in E3/2 heterozygotes relative to E3/3 patients. Baseline concentrations of low-density lipoprotein (LDL) cholesterol in untreated FH patients were not influenced by the apo E phenotype; the hypolipidemic response to lovastatin (20 or 40 mg twice daily) was also independent of the apo-E phenotype of the patients.