Gonadal hormones may exert permanent organizational effects on sexually dimorphic finger-length ratios and sexually dimorphic behavior expressed in childhood attention deficit-hyperactivity disorder (ADHD). This study extended recent work examining associations between finger-length ratios (specifically, 2D:4D) and ADHD in a well-characterized, clinically diagnosed, communityrecruited sample of boys and girls. A multistage, diagnostic procedure was utilized to identify 113 children with ADHD and 137 non-ADHD comparison children. Right-hand digit ratios showed significant mean differences by gender, as well as associations with ADHD diagnosis. Boys with ADHD had more masculinized digit ratios than control-group boys. More masculine right 2D:4D and 3D:4D ratios were correlated with parent-and teacher-rated inattentive and hyperactiveimpulsive symptoms in boys but not in girls. Masculinized finger-length ratios were associated with hyperactive-impulsive and oppositional-defiant symptoms, but associations were largest with symptoms of inattention. It is concluded that prenatal, organizational effects of gonadal hormones may play a role in the development of ADHD and contribute to explaining sex differences in the prevalence rates of this childhood disorder.
Keywordstestosterone; finger-length ratio; 2D:4D; ADHD; sex differences Males are more vulnerable than females to developing a range of learning and behavioral disorders during childhood. Attention deficit-hyperactivity disorder (ADHD) is one of the most common and impairing sexually dimorphic clinical psychopathologies, with boys about three times more likely to be identified with ADHD than girls in population samples (American Psychiatric Association, 2000;Pastor & Reuben, 2002;Wolraich, Hannah, Baumgaertel, & Feurer, 1998). In addition, there may be sex differences in the correlates of the disorder. Although boys with ADHD appear to be more inattentive and hyperactive-impulsive than girls with the disorder, particularly in school (Gaub & Carlson, 1997;Gershon, 2002;Hartung et al., 2002), girls with ADHD may have worse cognitive impairment than boys with the disorder (Biederman et al., 1999;Gaub & Carlson, 1997;Newcorn et al., 2001). The precise neurobiological mechanisms underlying sex differences in the prevalence rates of developmental learning and behavioral disorders are complex and underresearched.The male sex bias in ADHD and its precursor behaviors is apparent during early preschool years (Hart, Lahey, Loeber, Applegate, & Frick, 1995), a period marked by rapid neural organization (Breedlove & Hampson, 2002). Males are typically exposed to testosterone perinatally, whereas females develop in the relative absence of testosterone (Morris, Jordan, & Breedlove, 2004). This differential exposure to steroid hormones produces specific malelike and/or female-like brain-behavior patterns . Therefore, these prenatal events may be related to sex differences in prevalence rates of ADHD. However, research on hormonal effects in ADHD is sparse, despite conse...