Increased aggression and activity level in 3- to 11-year-old girls with congenital adrenal hyperplasia (CAH).

Experimental research in a wide range of mammals has documented powerful influences of androgen during early development on brain systems and behaviors that show sex differences. Clinical research in humans suggests similar influences of early androgen concentrations on some behaviors, including childhood play behavior and adult sexual orientation. However, findings have been inconsistent for some other behaviors that show sex differences, including aggression and activity level in children. This inconsistency may reflect small sample sizes and assessment limitations. In the present study, we assessed aggression and activity level in 3- to 11-year-old children with CAH (38 girls, 29 boys) and in their unaffected siblings (25 girls, 21 boys) using a questionnaire that mothers completed to indicate current aggressive behavior and activity level in their children. Data supported the hypotheses that: (1) unaffected boys are more aggressive and active than unaffected girls; (2) girls with CAH are more aggressive and active than their unaffected sisters; and (3) boys with and without CAH are similar to one another in aggression and activity level. These data suggest that early androgens have a masculinizing effect on both aggressive behavior and activity level in girls.