Abstract
Despite significant progress in understanding the mechanisms by which the prenatal/maternal environment can alter development and adult health, genetic influences on normal variation in growth are little understood. This work examines genetic and nongenetic contributions to body weight and weight change during infancy and the relationships between weight change and adult body composition. The dataset included 501 white infants in 164 nuclear and extended families in the Fels Longitudinal Study, each with 10 serial measures of weight from birth to age 3 years and 232 with body composition data in midβadulthood. Heritability and covariate effects on weight and weight zβscore change from birth to 2 years of age were estimated using a maximum likelihood variance decomposition method. Additive genetic effects explained a high proportion of the variance in infant weight status (h^2^ = 0.61β0.95), and change in weight zβscore (h^2^ = 0.56β0.82). Covariate effects explained 27% of the phenotypic variance at 0β1 month of age and declined in effect to 6.9% of phenotypic variance by 36 months. Significant sex, gestational age, birth order, birth year, and maternal body mass index effects were also identified. For both sexes, a significant increase in weight zβscore (β«2 SD units) (upward centile crossing) was associated with greater adulthood stature, fat mass, and percent body fat than decrease or stability in weight zβscore. Understanding genetic influences on growth rate in a wellβnourished, nutritionally stable population may help us interpret the causes and consequences of centile crossing in nutritionally compromised contexts. Am. J. Hum. Biol., 2007. Β© 2007 WileyβLiss, Inc.