Physiological evidence of hypermasculinization in boys with the inattentive type of attention-deficit/hyperactivity disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is more common in boys than in girls, suggesting that prenatal androgen exposure may play a role in etiology. Click-evoked otoacoustic emissions (CEOAEs) and relative finger length are measures known to exhibit sex differences early in life, also suggesting that prenatal androgen exposure plays a contributing role. CEOAEs and the lengths of the fingers were measured in boys and girls aged 7-15 who were diagnosed as having different types of ADHD. All six possible pairwise length ratios were calculated for the four fingers of each hand. The CEOAEs measured in boys diagnosed as ADHD/Inattentive were substantially smaller than those of either the boys diagnosed as ADHD/Combined or the Control boys, whose mean CEOAEs were alike. Similarly, most of the finger-length ratios (FLRs) were smaller for boys diagnosed as ADHD/Inattentive than for either ADHD/Combined or Control boys. Both of these outcomes represent a hypermasculinization of the boys diagnosed as ADHD/Inattentive. Thus, two quite different physiological measures suggest that these boys diagnosed as ADHD/Inattentive may have been exposed to higher-than-normal levels of androgens at some stage early in development. In accord with both Cantwell's proposal for validating psychiatric disorders and previous suggestions in the literature, these findings support the hypothesis that the Combined and Inattentive groups represent different disorders, not versions of a single disorder.