Serum lipids and apolipoprotein E phenotypes in identical twins reared apart.

Lipid and lipoprotein metabolism is controlled by genes, the environment and the gene environment interaction. We studied monozygotic twin pairs reared apart (MZA) and an age sex matched group of twins reared together (MZT) to evaluate the effects of the genotype and the rearing environment on lipids. The intraclass correlations for low density lipoprotein (LDL) cholesterol were 0.21 and 0.50 for the MZA and MZT groups, respectively, suggesting that the rearing environment possibly had an impact on the variability in LDL cholesterol later in life. The intraclass correlations for total cholesterol (0.26 and 0.47 for the MZA and MZT groups, respectively) reflected those for LDL cholesterol. The intraclass correlations for high density lipoprotein (HDL) cholesterol did not show any difference between the twin groups, suggesting that the rearing environment does not have major long-term effects on the variability of HDL levels. The intrapair differences for LDL cholesterol were smallest in the twins heterozygous for the apolipoprotein E allele epsilon2 (E2/3 and E2/4 phenotypes), intermediate in the pairs with the common E3/3 phenotype and enhanced in the pairs with E4/3 phenotype. To conclude, these data suggest that the rearing environment may play a role in the variability of LDL cholesterol levels, although variance difference between MZAs and MZTs, and the small number of available monozygotic twins reared apart limits the generalizability of the results.