A quarterly publication of the Autism Research Institute

The Autism Research Review International is quarterly publication of the Autism Research Institute

Winter, 2016 | Number 1, Volume 30

New finding complicates “extreme male brain” theory

Researchers reporting on a new twin study say their findings add “an intriguing complication” to the extreme male brain hypothesis of autism spectrum disorders (ASD). This hypothesis posits that high levels of testosterone in the womb are associated with higher levels of autistic and attention deficit hyperactivity disorder (ADHD) traits in children. 

In the new study, Jonna Maria Eriksson and colleagues analyzed data gathered from parents of more than 16,000 fraternal twins using the Autism-Tics, ADHD, and other Comorbidities inventory (A-TAC). “Assuming that having a male co-twin increases the prenatal exposure to testosterone,” they say, “the prenatal androgenization theory of autism would predict a higher rate of autistic traits in females with a male co-twin.” The same should also hold true, they say, for ADHD. 

“Instead,” they say, “the opposite result was found, that girls with a female co-twin were reported to have more ADHD and autistic traits than girls with a male co-twin. It was also significantly more common for boys and girls with a female co-twin to reach the lower cut-off for ADHD than for those with a male co-twin.” The latter pattern also was seen for ASD, but did not reach statistical significance. 

The researchers say their findings neither support nor refute the extreme male brain hypothesis, noting that a number of complex factors could account for their unexpected findings.


“Effect of co-twin gender on neurodevelopmental symptoms: a twin register study,” Jonna Maria Eriksson, Sebastian Lundström, Paul Lichtenstein, Susanne Bejerot, and Elias Eriksson, Molecular Autism, January 19, 2016 (online). Address: Jonna Maria Eriksson, jonna.erik [email protected].