Apolipoprotein E polymorphism influences lipid phenotypes in Chinese families with familial combined hyperlipidemia

Familial combined hyperlipidemia is a polygenic trait

PURPOSE OF REVIEW

: Familial combined hyperlipidemia (FCH), defined by concurrently elevated plasma triglyceride (TG) and low-density lipoprotein (LDL) cholesterol, has long been investigated to characterize its genetic basis. Despite almost half a century of searching, a single gene cause for the phenotype has not yet been identified.

RECENT FINDINGS

: Recent studies using next-generation genetic analytic methods confirm that FCH has a polygenic basis, with a clear large contribution from the accumulation of small-to-moderate effect common single nucleotide polymorphisms (SNPs) throughout the genome that is associated with raising TG, and probably also those raising LDL cholesterol. On the other hand, rare monogenic variants, such as those causing familial hypercholesterolemia, play a negligible role, if any. Genetic profiling suggests that patients with FCH and hypertriglyceridemia share a strong polygenic basis and show a similar profile of multiple TG-raising common SNPs.

SUMMARY

: Recent progress in genomics has shown that most if not all of the genetic susceptibility to FCH is polygenic in nature. Future research should include larger cohort studies, with wider ancestral diversity, ancestry-specific polygenic scores, and investigation of epigenetic and lifestyle factors to help further elucidate the causative agents at play in cases where the genetic etiology remains to be defined.

The genetics of familial combined hyperlipidaemia

Almost 40 years after the first description of familial combined hyperlipidaemia (FCHL) as a discrete entity, the genetic and metabolic basis of this prevalent disease has yet to be fully unveiled. In general, two strategies have been applied to elucidate its complex genetic background, the candidate-gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL or its related traits, with a variable degree of scientific evidence. Some genes influence the FCHL phenotype in many pedigrees, whereas others are responsible for the affected state in only one kindred, thereby adding to the genetic and phenotypic heterogeneity of FCHL. This Review outlines the individual genes that have been described in FCHL and how these genes can be incorporated into the current concept of metabolic pathways resulting in FCHL: adipose tissue dysfunction, hepatic fat accumulation and overproduction, disturbed metabolism and delayed clearance of apolipoprotein-B-containing particles. Genes that affect metabolism and clearance of plasma lipoprotein particles have been most thoroughly studied. The adoption of new traits, in addition to the classic plasma lipid traits, could aid in the identification of new genes implicated in other pathways in FCHL. Moreover, systems genetic analysis, which integrates genetic polymorphisms with data on gene expression levels, lipidomics or metabolomics, will attribute functions to genetic variants in addition to revealing new genes.

Genetic variation of apolipoprotein E does not contribute to the lipid abnormalities secondary to childhood minimal change nephrotic syndrome

Minimal change nephrotic syndrome (MCNS) is a common progressive renal disorder occurring in childhood that is characterized by alterations of permselectivity at the glomerular capillary wall, resulting in its inability to restrict the urinary loss of protein. Hyperlipidemia (HLP) is not only an important clinical manifestation of MCNS but is also involved in cardiovascular disease and in progressive renal damage. ApoE is a polymorphic protein. Besides modulation of lipid metabolism, apoE can also elevate the sulfate-proteoglycan in glomerular filtration membrane and inhibit the proliferation of mesengial cells. The present study aimed mainly to determine whether genetic polymorphism of apoE is involved in the HLP secondary to childhood MCNS. Genomic DNA was extracted from 250 children diagnosed with MCNS and 200 healthy controls. ApoE genotype was determined by PCR-restriction fragment length polymorphism (RFLP) analysis. The fasting serum lipoprotein (a) [Lp(a)], total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (apoA1), and apoB were measured. Serum concentrations of Lp(a), TC, TG, HDL-C, nonHDL-C, LDL-C, and apoB were higher in the MCNS than in the control group (P < 0.05). No significant differences in genotypes and alleles frequencies were observed for the apoE Hha I restriction sites in MCNS patients as compared to controls (P > 0.05). No significant differences in serum lipid levels were observed for variant genotypes and alleles of apoE Hha I restriction site in both MCNS and healthy children (P > 0.05). Genetic variation of apoE does not contribute to the lipid abnormalities secondary to childhood MCNS.

Apolipoprotein E polymorphism in normal Han Chinese population: frequency and effect on lipid parameters

Apolipoprotein E (ApoE) genotypes were studied in order to determine the prevalence and effect on lipid parameters in normal Han Chinese population. Fragments of ApoE gene forth exon containing codon 112 and 158 polymorphic locus were amplified by PCR, and then digested with Cfo I endonuclease. Genotypes and alleles frequencies of 168 healthy Han Chinese were calculated. The frequency of genotypes epsilon3/3, epsilon3/4, and epsilon2/3 was found to be 75.00, 10.70, and 11.90%, respectively, and 0.60, 1.20, and 0.60% for epsilon2/2, epsilon2/4, and epsilon4/4. The effects of ApoE genotypes and alleles on lipid parameters were analyzed. The effects of ApoE alleles on TC, LDL-C, ApoB was: along a decreasing gradient epsilon4 > epsilon3 > epsilon2. The effect of epsilon4 allele was to increase serum levels of TC, LDL-C and ApoB, and epsilon2 allele had an effect opposite to that of epsilon4 allele. Results obtained in this study indicate that ApoE polymorphism is an independent genetic factor on individual serum levels of lipids and apolipoproteins.

Relation of apolipoprotein E polymorphism to markers of early atherosclerotic changes in young adults--the Cardiovascular Risk in Young Finns Study

BACKGROUND

Carotid artery intima-media thickness (IMT), which is measured by ultrasound, is used in the assessment of early atherosclerotic changes, and has been associated with apolipoprotein E (APOE) polymorphism in many studies comprising elderly subjects. However, results are still inconclusive and data relating to young adults are missing. Whether common APOE polymorphism is related to carotid IMT was studied in a population of young adults. Also brachial flow-mediated dilatation (FMD) and carotid artery compliance (CAC) were determined to clarify their relation to this genetic factor.

METHODS AND RESULTS

A total of 1,188 young adults (aged 24-39 years) participating in the Cardiovascular Risk in Young Finns Study with complete data of common APOE polymorphism underwent a carotid and brachial ultrasound. Patients' lipid levels and blood pressure were also examined. There was no significant association between the APOE phenotypes and carotid IMT, brachial FMD or CAC either in young men or in young women. The results were similar for systolic and diastolic blood pressure. In the same population, the well-known association between APOE phenotypes and lipids was seen.

CONCLUSIONS

Common APOE polymorphism does not seem to be an independent genetic determinant of carotid IMT, brachial FMD or CAC.