Common low-density lipoprotein receptor p.G116S variant has a large effect on plasma low-density lipoprotein cholesterol in circumpolar inuit populations

Abstract

Background: Inuit are considered to be vulnerable to cardiovascular disease because their lifestyles are becoming more Westernized. During sequence analysis of Inuit individuals at extremes of lipid traits, we identified 2 nonsynonymous variants in low-density lipoprotein receptor (LDLR), namely p.G116S and p.R730W.

Methods and results: Genotyping these variants in 3324 Inuit from Alaska, Canada, and Greenland showed they were common, with allele frequencies 10% to 15%. Only p.G116S was associated with dyslipidemia: the increase in LDL cholesterol was 0.54 mmol/L (20.9 mg/dL) per allele (P=5.6×10(-49)), which was >3× larger than the largest effect sizes seen with other common variants in other populations. Carriers of p.G116S had a 3.02-fold increased risk of hypercholesterolemia (95% confidence interval, 2.34-3.90; P=1.7×10(-17)), but did not have classical familial hypercholesterolemia. In vitro, p.G116S showed 60% reduced ligand-binding activity compared with wild-type receptor. In contrast, p.R730W was associated with neither LDL cholesterol level nor altered in vitro activity.

Conclusions: LDLR p.G116S is thus unique: a common dysfunctional variant in Inuit whose large effect on LDL cholesterol may have public health implications.

Keywords: cardiovascular diseases; genetic variation; low-density lipoprotein cholesterol.

Figure 1. LDLR variant associations with LDL cholesterol (C) in a combined Inuit cohort

Inuit participants were separated based on LDLR p.G116S or p.R730W genotype and LDL cholesterol concentration. A) Frequency distribution of Inuit participants based on p.G116S carrier status and LDL cholesterol concentration. Mean LDL cholesterol concentrations between non-carriers (GG, n=2585), heterozygotes (GA, n=559) and homozygotes (AA, n=53) were compared using one-way ANOVA with the P-value as indicated. B) Frequency distributions were similarly constructed for p.R730W non-carriers (CC, n=2408), heterozygotes (CT, n=717) and homozygotes (TT, n=72) and were also compared using one-way ANOVA.

Figure 2. Association between Inuit LDLR variants and very elevated LDL cholesterol (C) concentration

Forest plots indicate odds ratios (OR) and 95% confidence intervals (95% CI) from association testing between both LDLR p.G116S or p.R730W variant genotypes and severely elevated LDL cholesterol status (LDL cholesterol >5.0 mmol/L).

Figure 3. Comparison of LDLR expression and ligand binding ability between wild-type and Inuit-identified variants

A) COS7 cells were transfected with expression vectors encoding Myc-DDK-tagged LDLR and LDLR variants mutated to recreate the Inuit-identified polymorphisms or established LDLR variants previously reported. Total cell lysates were analysed and transfections for this model were performed twice. B) LDLR binding activity was measured in HepG2 cells and normalized based on expression data from the corresponding mature LDLR isoforms. Binding activity experiments were performed in triplicate at two doses of LDL and were averaged. Average binding activity estimates were then normalized based on the expression data determined from either the Myc-DDK-tagged, GFP-tagged, or combined GFP- and Myc-DDK-tagged expression models. Error bars represent normalized standard error. All binding read-outs for p.G116S transfectants are significantly different from wild-type (all P<0.05) while none of the read-outs for p.R730W transfectants are significantly different from wild-type (all P >0.05).