Examining the genetic relationship of attention deficit and hyperactivity disorder and conduct disorder in a population-based twin sample

Abstract

Objective To examine three possible causes of the relationship between attention deficit and hyperactivity disorder (HYPER) and conduct disorder (COND) : additive genetic factors (A), common environmental factors (C) and individual-specific environmental factors(E). Methods 140 pairs of twins from the Southwestern China Twin Registry were examined with the parent-rated Strength and difficulties questionnaire (SDQ). The cress-twin within-variable, within-twin croas-variable and croas-twin crossvariable correlations were calculated. Using structural equation modelling, bivariate models were fitted. The best fitting model was chosen based on likelihood and parsimony. Results The correlation between attention deficit and hyperactivity behavior and conduct behavior in monozygotic twins (r=0.55) was significantly higher than that in dyzygotic twins (r=0.12). The observed phenotypic correlation between HYPER and COND was 0.44 (P=0.00), with genetic factors accounting for about 70% of the observed correlation. Conclusions h children, three different genetic factors may exist: one that solely affects the liability to hyperactivity behavionr, one that has only an effect on conduct behaviour and one that influences beth hyperactivity and conduct behaviour. Our results suggests that most of the environmental factors that increase the risk of hyperactivity behaviour do not influence conduct behaviour and vice versa. Key words: Attention deficit disorder with hyperactivity;  Twin studies;  Heredity; Environment