Attention deficit/hyperactivity disorder (ADHD) symptoms and digit ratios in a college sample

Diagnosticians recognize three subtypes of attention deficit/hyperactivity disorder (ADHD) if there are developmentally inappropriate levels (six or more symptoms) of Hyperactive-Impulsive behavior, or Inattentive behavior, or both (Combined), respectively. ADHD may partly reflect androgen dysfunction, and an arguable proxy for prenatal androgen exposure is the 2D:4D finger ratio set at least as early as week 9 in the fetus; this is lower in men than in women. We examined the relationship between digit ratios and ADHD symptoms representing the three phenotypes: ADHD/Combined as measured by "summarized" (Rasched) scales, i.e., 1) the short version of the Wender Utah Rating Scale (WURS) and a total symptom list derived from the DSM IV, and the subdivided DSM IV into 2) ADHD/Inattentive and 3) ADHD/Hyperactive-Impulsive inventories, in a sample of European-descent college students (135 female, 52 male) not selected for ADHD. All digit ratios were calculated excluding the thumb. There were significant sex differences for the 2D:4D digit ratios of both hands (RH and LH), and between the RH 3D:4D and between the LH 2D:3D ratio. In females, the more masculine the LH 2D:4D ratio, the more the ADHD/Combined symptoms (both WURS and DSM) and the more the ADHD/Inattentive symptoms and ADHD/Hyperactive-Impulsive symptoms. More masculine ratios also correlated between the total WURS and RH 2D:3D, RH 2D:4D, and LH 2D:3D; and between the inattentive DSM symptoms and LH 2D:5D, and between the ADHD/Hyperactive and Impulsive symptoms and RH 3D:4D.