GENETIC AND ENVIRONMENTAL-FACTORS IN RELATIVE BODY-WEIGHT AND HUMAN ADIPOSITY

We review the literature on the familial resemblance of body mass inde x (BMT) and other adiposity measures and and strikingly convergent res ults for a variety of relationships. Results from twin studies suggest that genetic factors explain 50 to 90% of the variance in BMI. Family studies generally report estimates of parent-offspring and sibling co rrelations in agreement with heritabilities of 20 to 80%. Data from ad option studies are consistent with genetic factors accounting for 20 t o 60% of the variation in BMI. Based on data from more than 25,000 twi n pairs and 50,000 biological and adoptive family members, the weighte d mean correlations are .74 for MZ twins, .32 for DZ twins, .25 for si blings, .19 for parent-offspring pairs, .06 for adoptive relatives, an d .12 for spouses. Advantages and disadvantages of twin, family, and a doption studies are reviewed. Data from the Virginia 30,000, including twins and their parents, siblings, spouses, and children, were analyz ed using a structural equation model (Stealth) which estimates additiv e and dominance genetic variance, cultural transmission, assortative m ating, nonparental shared environment, and special twin and MZ twin en vironmental variance. Genetic factors explained 67% of the variance in males and females, of which half is due to dominance. A small proport ion of the genetic variance was attributed to the consequences of asso rtative mating. The remainder of the variance is accounted for by uniq ue environmental factors, of which 7% is correlated across twins. No e vidence was found for a special MZ twin environment, thereby supportin g the equal environment assumption. These results are consistent with other studies in suggesting that genetic factors pray a significant ro le in the causes of individual differences in relative body weight and human adiposity.