Effects of intragenic variability at 3 polymorphic sites of the apolipoprotein B gene on serum lipids and lipoproteins in a multiethnic Asian population

We determined the allelic (X+/X-, M+/M-, and E+/E-) distribution frequencie s of the XbaI, MspI, and EcoRI restriction fragment length polymorphisms (R FLPs) in the apolipoprotein B gene in a control group of 374 healthy Chines e, Malays, and Indians and in a hyperlipidemic cohort of 131 Chinese patien ts. Covariability between the RFLPs and serum lipid, lipoprotein, and apoli poprotein concentrations was also studied. We found a lower frequency (aver age 0.0829) of the X+ allele and higher frequencies of the Ef (average 0.94 52) and M+ (average 0.9772) alleles in our study population compared with f requencies reported in other populations. The 3 polymorphic sites did not c ontribute to significant variations in lipid levels (p > 0.1 in all cases). Also, there was no significant variation in genotype frequencies between t he control subjects and the hyperlipidemic subjects. Despite their relative close proximity within the APOB gene sequence, the 3 poly morphic sites di d not show any significant linkage disequilibrium. However, the presence of the X+ cutting site was in linkage disequilibrium with the Del allele of t he 5' insertion-deletion polymorphism and the E-allele was in linkage diseq uilibrium with the 3' VNTR located near the 3' end of the coding region of the APOB gene.