LETTER TO JMG Association of genetic variants in the HDL receptor, SR-B1, with abnormal lipids in women with coronary artery disease

Plasma lipid concentrations are complex traits having both environmental and genetic determinants. About half of the variation in HDL-C and TG may be genetic with the same genes possibly accounting for the correlated traits of LDL particle size, TG, and HDL-C. A number of variants in candidate genes have been implicated in the regulation of plasma lipid levels. In addition, genome scans have identified chromosomal regions with suggestive linkage to the TG:HDL-C ratio and other lipid parameters. 7 Nonetheless, much of the genetic variability in HDL-C and TG levels remains unexplained. Decreased HDL cholesterol (HDL-C) and raised triglyceride (TG) levels are well known risk factors for the development of coronary artery disease (CAD) and atherosclerosis. Plasma TG and HDL-C levels are highly correlated, but there is some evidence that they may exert independent effects on coronary disease risk. Indeed, the simultaneous use of both may more accurately predict risk of coronary disease. Among patients with low HDL-C, risk of CAD was more than doubled in those with concurrent high TG compared to those with low TG levels in both the PROCAM and Helsinki Heart studies. Furthermore, the ratio of TG:HDL-C has been shown to correlate with LDL particle size and is a powerful predictor of future myocardial infarction. The scavenger receptor class B type 1, SR-B1, is a key component in the reverse cholesterol transport pathway where it binds HDL-C with high affinity and is involved in the selective transfer of lipids from HDL-C. 15 It is expressed primarily in liver and non-placental steroidogenic tissues and mediates selective cholesterol uptake by a mechanism distinct from the classical low density lipoprotein cholesterol (LDL-C) receptor pathway. Previous studies 18 have found single nucleotide polymorphisms (SNPs) in the gene for SR-B1, SCARB1, associated with plasma lipids. In one of these studies by our group, three populations of diabetic kindred showed an association between combinations of SNPs in SCARB1 and HDL-C that appeared to be modified by gender. We sought to confirm and extend these findings in a case series of patients with premature, familial CAD and therefore enriched for low HDL-C. The most common cause of low HDL-C associated with CAD is hypertriglyceridaemia. Accordingly, we chose to examine associations between SCARB1 SNPs and HDL-C, TG, and the TG:HDL-C ratio.