Female-to-male transsexual people have a higher than average number of autistic traits, says a new study.
The study from Cambridge University, funded by the Medical Research Council (MRC), has important implications for the clinical management of biological girls with gender incongruence that persists into adulthood, and for the "extreme male brain" theory of autism.
Professor Simon Baron-Cohen, Director of the Autism Research Centre at University of Cambridge, led the study with Rebecca Jones, now at Weill Cornell Graduate School of Medical Sciences.
The researchers measured autistic traits using the Autism Spectrum Quotient (AQ), and compared AQ scores from five groups: 61 transmen, 198 transwomen; 76 typical males; 98 typical females; and 125 individuals with Asperger Syndrome (AS).
They found transmen had a higher average AQ than typical females, typical males and transwomen, but lower than individuals with AS.
"Girls with a higher than average number level of autistic traits tend to have male-typical interests, showing a preference for systems over emotions," Baron-Cohen interpreted the results.
"They prefer not to socialise with typical girls because they have different interests, and because typical girls on average have more advanced social skills.
"Both of these factors may lead girls with a higher number of autistic traits to socialize with boys, to believe they have a boy's mind in a girl's body, and to attribute their unhappiness to being a girl," he stated.
The team included Professor Richard Green and Dr Domenico Di Ceglie, world experts in transsexualism and gender incongruence in young people respectively, and by Emma Martin, a clinical psychotherapist and herself transsexual.
Jones added: "If such girls do believe they have a boy's mind in a girl's body, their higher than average number of autistic traits may also mean they hold their beliefs very strongly, and pursue them to the logical conclusion: opting for sex reassignment surgery in adulthood."
Di Ceglie, Director of Training and Research at the Gender Identity Development Service at the Tavistock and Portman NHS Foundation Trust in London, said: "These are important findings in the field of gender incongruence, which need to be replicated."
"The awareness of the presence of autistic features may help these young people to explore the reasons behind their perceptions, and help them make more informed decisions about treatment," he said.
Emma Martin, who runs a Gender Identity Support and research group in Little Downham, UK, welcomed the new findings.
"This new research reminds us that gender incongruence is incredibly complex," she warned.
"Every possibility should be discussed with new clients, but should not delay what can be a painfully slow process for those affected," she added.
The story has been published in the Journal of Autism and Developmental Disorders.