GENETICS AND DEVELOPMENTAL PSYCHOPATHOLOGY .2. THE MAIN EFFECTS OF GENES AND ENVIRONMENT ON BEHAVIORAL-PROBLEMS IN THE VIRGINIA TWIN STUDY OF ADOLESCENT BEHAVIORAL-DEVELOPMENT

Little is known about the contribution of genetic and environmental fa ctors to risk for juvenile psychopathology. The Virginia Twin Study of Adolescent Behavioral Development allows these contributions to be es timated. A population-based, unselected sample of 1412 Caucasian twin pairs aged 8-16 years was ascertained through Virginia schools. Assess ment of the children involved semi-structured face-to-face interviews with both twins and both parents using the Child and Adolescent Psychi atric Assessment (CAPA). Self-report questionnaires were also complete d by parents, children, and teachers. Measures assessed DSM-III-R symp toms of Attention Deficit Hyperactivity Disorder (ADHD), Conduct Disor der, Oppositional Defiant Disorder, Overanxious Disorder, Separation A nxiety, and Depressive Disorder. Factorially derived questionnaire sca les were also extracted. Scores were normalized and standardized by ag e and sex. Maximum likelihood methods were used to estimate contributi ons of additive and nonadditive genetic effects, the shared and unique environment, and sibling imitation or contrast effects. Estimates wer e tested for heterogeneity over sexes. Generally, monozygotic (MZ) twi ns correlated more highly than dizygotic (DZ) twins, parental ratings more than child ratings, and questionnaire scales more highly than int erviews. DZ correlations were very low for measures of ADHD and DZ var iances were greater than MZ variances for these variables. Correlation s sometimes differed between sexes but those for boy-girl pairs were u sually similar to those for like-sex pairs; Most of the measures showe d small to moderate additive genetic effects and moderate to large eff ects of the unique individual environment. Measures of ADHD and relate d constructs showed marked sibling contrast effects. Some measures of oppositional behavior and conduct disorder showed shared environmental effects. There were marked sex differences in the genetic contributio n to separation anxiety, otherwise similar genetic effects appear to b e expressed in boys and girls. Effects of rater biases on the genetic analysis are considered. The study supports a widespread influence of genetic factors on risk to adolescent psychopathology and suggests tha t the contribution of different types of social influence may vary con sistently across domains of measurement.