Apparent influence of marker genotypes on variation in serum cholesterol in monozygotic twins.

Ninety-seven monozygotic (MZ) twin pairs were grouped by marker system genotypes, and mean intrapair differences in serum total cholesterol level were compared between groups. Significant differences were found when the MNs and the Kidd blood group systems were considered. The results appear to suggest a restrictive effect of certain normal marker genes on environmentally caused variation in serum cholesterol level.