Linkage analysis of candidate genes and the small, dense low-density lipoprotein phenotype

There is accumulating evidence for the importance of small, dense low-densi ty lipoprotein (LDL), the defining feature of the atherogenic lipoprotein p henotype, as a risk factor for coronary heart disease. Although both family studies and twin studies have demonstrated genetic influences on this phen otype, the specific gene(s) involved remain to be identified. The purpose o f this study was to determine whether there was evidence for genetic linkag e between small, dense LDL (LDL subclass phenotype B), as determined by gra dient gel electrophoresis, and selected candidate genes known to be involve d in lipid metabolism. The linkage analyses were based on a sample of 19 fa milies, including 142 individual family members, using a lod score linkage analysis approach. Nine candidate genes were examined, including loci for m anganese superoxide dismutase (Mn SOD2), apolipoproteins CIII, AII, and apo CII, lipoprotein lipase, hepatic lipase, microsomal triglyceride transport protein, the insulin receptor and the LDL receptor. The analyses did not p rovide significant evidence for genetic linkage between markers for any of these genes and LDL subclass phenotype B, nor did it confirm previous repor ts of linkage between the LDL receptor gene and LDL subclass phenotype B. U sing three closely linked markers for the Mn SOD2 locus excluded close link age between this candidate gene region and LDL subclass phenotype B. These findings demonstrate the complexity of genetically mapping risk factor phen otypes, and emphasize the necessity of identifying new genetic loci, other than known candidate genes, involved in susceptibility to atherosclerosis. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.