When autism is mentioned, that mention will almost certainly include a statistic. One of the more common autism-related numbers thrown around these days is the fact that it is four times more likely to occur in boys than in girls. A less commonly discussed phenomenon in the autism community (and in the greater mental health community) is that autism spectrum disorders (ASD) occur at a higher rate in transgender people than in the general population. This trend, documented in dozens of case studies and prevalence studies, causes some uncertainty around the four-times-more-common-in-males statistic and raises questions about autism and gender identity.

A study conducted by a team of British scientists in 2012 found that of a pool of individuals not diagnosed on the autism spectrum, female-to-male (FTM) transgender people have higher rates of autistic features than do male-to-female (MTF) transgender people or cisgender males and females. Another study, which looked at children and adolescents admitted to a gender identity clinic in the Netherlands, found that almost 8 percent of subjects were also diagnosed with ASD. That figure is nearly four times higher than the rate of ASD in the general population, according to the Centers for Disease Control and Prevention (CDC). Turkish researcher N. M. Mukaddes suggests that this number may even be low, citing the fact that individuals with lower levels of language may be unable to communicate their feelings of dissatisfaction with their assigned gender.

A core theory of autism is that it is an exaggeration of the typically male characteristic of systemizing with a low level of empathizing, considered a female characteristic. Called the extreme male brain (EMB) theory of autism, this theory developed from a body of research that found that males typically exhibit higher performance on tasks designed to test systemization, and lower performance on tasks measuring empathy. The British researcher who originally published this theory, Simon Baron-Cohen, applied it to individuals on the autism spectrum, observing that individuals with ASD generally perform even higher on systemization tasks than do neurotypical males, hence the term "extreme male brain." As bizarre as these findings may sound, they have been supported by several other studies looking at sex and ASD. However, this theory has been criticized as being based on an "unpersuasive gendering of certain capacities or aptitudes in the human population," Timothy Krahn and Andrew Fenton wrote. Krahn and Fenton go even further to suggest that this theory may inadvertently favor males in the diagnostic process, thereby reducing access to services by females with symptoms of ASD.

While the EMB theory focuses on cognitive abilities, other factors related to sex and gender have been found to correlate with ASD. An international team of researchers found significantly higher levels of male hormones in both males and females diagnosed with ASD than in the neurotypical control group. These findings raise questions regarding both ASD and gender nonconformity. For example, could higher levels of male hormones be the cause of both ASD and feelings of gender dysphoria (the newly published clinical term for being transgender)? Or could the presence of one cause the higher levels of hormones, which in turn causes the other? Is it only more masculine women who are diagnosed with ASD, while others who show symptoms go undiagnosed? Only time and much more research on the topic will reveal the answers to these questions.

One thing we do know for sure is that transgender individuals with ASD need an extra level of treatment. Research has found that transgender individuals diagnosed with developmental disabilities are at increased risk of sexually unhealthy behavior. The authors of that study suggest that caretakers' efforts to protect these individuals may inadvertently limit their autonomy and push them toward riskier sexual behavior. Therefore, it is important that people providing care to these unique individuals remain mindful of the unique needs and limitations that they face.

Special thanks to the Center for Gender, Sexuality and HIV Prevention at the Ann & Robert H. Lurie Children's Hospital of Chicago for assistance with resources.