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We determined the allelic (X + /X - , M + /M - , and E + /E - ) distribution frequencies of the Xbal, MspI, and EcoKl restriction fragment length polymorphisms (RFLPs) in the apolipoprotein B gene in a control group of 374 healthy Chinese, Malays, and Indians and in a hyperlipidemic cohort of 131 Chinese patients. Covariability between the RFLPs and serum lipid, lipoprotein, and apolipoprotein concentrations was also studied. We found a lower frequency (average 0.0829) of the X+ allele and higher frequencies of the E+ (average 0.9452) and M+ (average 0.9772) alleles in our study population compared with frequencies reported in other populations. The 3 polymorphic sites did not contribute to significant variations in lipid levels (p > 0.1 in all cases). Also, there was no significant variation in genotype frequencies between the control subjects and the hyperlipidemic subjects. Despite their relative close proximity within the APOB gene sequence, the 3 polymorphic sites did not show any significant linkage disequilibrium. However, the presence of the X + cutting site was in linkage disequilibrium with the Del allele of the 5' insertion-deletion polymorphism and the E — allele was in linkage disequilibrium with the 3' VNTR located near the 3' end of the coding region of the APOB gene.