A twin-sibling study of tobacco use in adolescence: etiology of individual differences and extreme scores.

A database is emerging that examines the relative contributions of genes and the environment to the etiology of smoking in adolescence. We present analyses derived from a genetically informative subsample of sibling pairs (monozygotic and dizygotic twins, full siblings, and half-siblings) participating in two waves of the National Longitudinal Study of Adolescent Health to estimate these parameters on both individual differences in smoking and extreme levels of smoking. Evidence indicated both genetic and shared environmental influences on high levels of smoking frequency, as well as on individual differences in smoking. No notable gender differences in these parameters emerged. Shared environmental effects were especially notable for high levels of smoking frequency and significantly greater than those found for individual differences. These findings were compatible with prior studies of both adolescent and adult smoking and reinforce the importance of familial influences on high levels of smoking frequency in adolescence.