It is worth noting that the heritability estimates of conduct disorder reviewed here are at the aggregate symptom level. At the phenotypic level, researchers have distinguished between aggressive and non-aggressive subtypes of conduct disorder (Loeber et al., 2000), raising the question of the degree to which these subtypes are heritable and have distinct or overlapping genetic etiology. According to a meta-analysis of clinical and non-clinical measures of antisocial behavior, the heritability of aggressive behavior (h2 = 0.65) is higher than the heritability of non-aggressive rule-breaking antisocial behavior (h2 = 0.48) (Burt, 2009). With respect to DSM-oriented studies of conduct disorder, in a community sample of 1,100 adolescent twin pairs, both the aggressive and non-aggressive domains were moderately heritable (49% and 55%, respectively) (Gelhorn et al., 2005). The phenotypic correlation between these domains was moderate (r = 0.32), and genetic influences accounted for a large proportion (61%) of the phenotypic correlation between aggressive and non-aggressive DSM-IV criteria (Gelhorn et al., 2006). However, criterion-level heritability analyses indicated that specific DSM-IV conduct disorder criteria (e.g., truancy) showed little to no heritability but rather
