GENETIC AND ENVIRONMENTAL-INFLUENCES ON SERUM-LIPID LEVELS IN TWINS

Background. The extent to which serum lipid levels are affected by gen etic and environmental tactors remains a point ot controversy. We exam ined both genetic and environmental influences on serum lipid levels i n twins reared either together or apart who participated in the Swedis h Adoption/Twin Study of Aging. Methods. We studied 302 pairs ot twins (mean age, 65.6 years; range, 52 to 86); 146 pairs had been reared ap art. We simultaneously compared the twins on the basis ot both zygosit y and rearing status, which allowed joint estimation of genetic and en vironmental influences on serum lipid levels. Genetic influence was ex pressed in terms of heritability, the proportion of the population var iation attributable to genetic variation (a value of 1.0 indicates tha t all of the population variation is attributable to genetic variation ). The serum lipids and apolipoproteins measured included total choles terol, high-density lipoprotein cholesterol, apolipoproteins A-I and B , and triglycerides. Results. Structural-equation analyses revealed su bstantial heritability for the serum levels of each lipid measured, ra nging from 0.28 to 0.78. Comparisons of the twins reared together with those reared apart suggested that the environment of rearing had a su bstantial impact on the level of total cholesterol (accounting for 0.1 5 to 0.36 of the total variance). Sharing the same environment appeare d to affect the other lipid measures much less, however, than did gene tic factors and unique environmental factors not shared by twins. Comp arisons of younger with older twins suggested that heritability for ap olipoprotein B and triglyceride levels decreased with age. Conclusions . The effect of genetic factors on the serum levels of some but not al l lipids appears to decrease with age. Early rearing environment appea rs to remain an important factor in relation to levels of total choles terol later in life, but it has less effect on other serum lipids and apolipoproteins in the elderly.