Reports of gender differences in the magnitude of genetic and environmental influences in twins have been mixed. Several studies report significant gender differences in the heritability of CD and antisocial behavior in general (Graham & Stevenson, 1985; Eley et al. 1999; Jacobson et al. 2002; Hudziak et al. 2003). By contrast, other studies have reported no gender differences in additive genetic and shared environment effects for CD (Eaves et al. 1997), adult antisocial behavior (Slutske et al. 1997; Rhee & Waldman, 2002) or CD symptoms (Gelhorn et al. 2005). Results from adoption studies are also varied with respect to gender differences of genetic and environmental effects. Some have reported that the same genetic factors are responsible for antisocial behaviors in both males and females (Cadoret & Cain, 1980), whereas others suggest greater genetic effects in female CD compared with males (Langbehn et al. 1998).
