Differences in finger length ratio between males with autism, pervasive developmental disorder–not otherwise specified, ADHD, and anxiety disorders

Children with autism have a relatively shorter index finger (2D) compared with their ring finger (4D). It is often presumed that the 2D:4D ratio is associated with fetal testosterone levels and that high fetal testosterone levels could play a role in the aetiology of autism. It is unknown whether this effect is specific to autism. In this study, 2D:4D ratios of 144 males aged 6 to 14 years (mean age 9y 1mo [SD 1y 11mo]) with psychiatric disorders were compared with those of 96 males aged 6 to 13 years from the general population (mean age 9y 1mo [SD 1y 10mo]). Psychiatric disorders were divided into autism/Asperger syndrome (n=24), pervasive developmental disorder–not otherwise specified (PDD–NOS; n=26), attention-deficit–hyperactivity disorder (ADHD)/oppositional defiant disorder (ODD; n=68), and anxiety disorders (n=26). Males with autism/Asperger syndrome (p