Analysis of genetic and environmental sources of variation in serum cholesterol in Tecumseh, Michigan--VI. A search for genotype by environment interaction.

We have examined 12 unlinked polymorphic genetic marker systems and found 6 which each identified small but statistically significant differences in normal serum cholesterol levels which did not change significantly with age. The effects associated with 4 of the 6-ABO. haptoglobin, Gm and secretor-were consistent in males and females and combined additively to define effects which were also homogeneous over age. There was a marker phenotype by age interaction effect on cholesterol variance in females but not in males. This study supports the hypothesis that a number of polymorphic genes, each with a small additive effect on cholesterol level. play an important role in determining cholesterol variability.