Further evidence that some male-based neurodevelopmental disorders are associated with high intrauterine testosterone concentrations.

It has been suggested that reading disability (RD), autism spectrum disorder (ASD), and attention-deficit-hyperactivity disorder (ADHD) share a measure of genetic overlap. They also share some epidemiological features, and have all been suspected of multifactorial (genetic and environmental) threshold origins. It has also been hypothesized that ASD, pervasive developmental disorder - not otherwise specified, and ADHD are partially caused by high maternal intrauterine testosterone levels. Here I offer a new method of testing this latter hypothesis on some of these disorders (RD, ADHD, and ASD). All these disorders occur more commonly in males. If the intrauterine testosterone hypothesis was correct, then probands should have a statistically significant excess of brothers among their siblings. Data are adduced here to test this. When treated as individual disorders, the data are significant only in the case of RD. However, the data are highly significant when pooled as RD + ADHD or RD + ADHD + ASD. Taken alone, the data on ASD are not significant. These results suggest that: (1) taxonomically, RD and ADHD are moresimilar to one another than either is to ASD; and (2) probands in the pooled samples have a very highly significant excess of brothers. This result stands in need of explanation. Provisionally, the data may be interpreted as suggesting that RD may be caused by high intrauterine testosterone levels, and confirming the hypothesis that ADHD is partially caused by high intrauterine testosterone.