Genetic analysis of a polymorphism in the human apolipoprotein A-I gene promoter: Effect on plasma HDL-cholesterol levels

Previous studies have indicated that a G to A substitution at position - 76 in the gene encoding apolipoprotein A-I (apoA-I) confers increased plasma high density lipoprotein cholesterol (HDL-C). Increased HDL-C may be a direct consequence of the A allele, or may reflect the action of a locus in linkage disequilibrium with the A allele. To elucidate this question, we examined the effect of this polymorphism in a large sample (n = 409) of unrelated Caucasians and their nuclear families (n = 22). To eliminate the confounding effects of hypertriglyceridemia, individuals with triglyceride levels greater than 150 mg/dl were excluded from the study. ApoA-I genotype was determined by polymerase chain reaction (PCR) amplification of genomic DNA and restriction digestion with Msp I. Individuals were grouped by genotype (GG, GA or AA) and mean adjusted HDL levels of the three groups were compared by one-way analysis of variance. Our analysis indicates that HDL-C levels do not vary by genotype, and no gene dosage effect is apparent in men or in women. Analysis of 22 informative Caucasian nuclear families showed no significant difference between individuals with the A allele and their GG siblings. These data suggest that polymorphism at -76 in the apoA-I gene does not directly affect HDL levels. Therefore, the increased HDL-C levels reported in other populations must reflect linkage disequilibrium between the A allele and a putative HDL-raising allele. As we find no evidence for association between the A allele and high HDL levels, this putative allele must occur at a low frequency in the population sampled in this study.