Finger length of boys with ASD differs from those with disruptive behavior, anxiety

Background: Over 125 years ago it was already shown that males had longer ring fingers relative to their index fingers, and women showed the reverse pattern. Since then, a large amount of studies have associated the length of the index finger relative to the length of the ring finger, the 2D:4D ratio, with a variety of variables (i.e., assertiveness, breast cancer, attractiveness, fertility, female waist-hip ratio, homosexuality). Finger length is determined by hormonal influences (testosterone) in the first 3 months of pregnancy and remains stable over life. Specific patterns of the 2D:4D ratio have been associated with autism before but the milder form of ASD, PDD-NOS, has not yet been studied and also it is unknown whether certain 2D:4D patterns are specific for ASDs.

Objectives: The aim of this study was to compare finger length in boys with different psychiatric disorders.

Methods: Vernier calipers were used to measure finger length in boys with anxiety disorders (n = 20), ADHD/ODD/CD (n = 60), autism/Asperger syndrome (n = 15), PDD-NOS (n = 60), and were compared to normal controls (n = 90). Only boys were included to rule out the effect of male-female differences in finger length, and the effect of a difference male-female prevalence for the disorders.

Results: Groups differed on 2D:4D ratio for the right hand only. Boys with autism/Asperger syndrome showed the most male-like 2D:4D pattern. They had a lower ratio than boys with PDD-NOS, anxiety disorders, and normal controls. Further, boys with externalizing disorders also showed a more male-oriented finger pattern, with a lower 2D:4D ratio than boys with anxiety disorders and normal control boys. The anxious boys showed the most female-like finger pattern compared to the other groups.

Conclusions: Finger length differs in child psychiatric groups which indicates that different underlying endocrinological factors might play a role.