ApoE polymorphism accounts for only part of the genetic variation in quantitative ApoE levels

ApoE levels and chromosome 19 ApoE polymorphisms were measured in a sample of 156 Dutch families. Each pedigree consisted of parents aged 35-65 years and their twin offspring aged 14-21 years. A significant effect of the chromosome 19 apoE locus on quantitative plasma levels of apolipoprotein E was observed. The ApoE polymorphism explained 16% of the variance in ApoE levels. Tests of association of ApoE levels with the apoC1 locus, which is in complete linkage disequilibrium with the ApoE locus, also showed a significant effect, although the variance explained by ApoC1 was only 1%. Examination of the covariance between twins classified according to allele sharing indicates that the association is not due to population stratification, but to a genuine effect of the ApoE locus on levels. However, the ApoE locus accounts for only one-fourth of the genetic variation in ApoE levels.