A study of genetic and environmental effects on the co-occurrence of problem behaviors in three-year-old twins

The authors examined the genetic and environmental causes of the co-occurre nce of problem behaviors in children. The analyses involved mother and fath er ratings of Oppositional, Withdrawn/Depressed. Aggressive, Anxious, Overa ctive, and Sleep Problems in 446 monozygotic and 912 dizygotic pairs of 3-y ear-old twins. Genetic factors contributed on average .150 (37.3%), shared environment .206 (51.2%), and nonshared environment .046 (11.4%) to the phe notypic correlations between the syndromes. Genetic and environmental facto rs caused different groupings Internalizing and Externalizing groupings wer e indicative of nonshared environmental factors; clusters of problem behavi ors with either the Aggressive or Anxious symptoms were most suggestive of genetic factors, and high scores on all syndromes indicated shared environm ental influences.