Sex and gender differences in autism exist regarding prevalence, presentation, and diagnosis. Men and boys are more frequently diagnosed with autism than women and girls. It is debated whether this is due to a sex difference in rates of autism spectrum disorders (ASD) or whether females are underdiagnosed. The prevalence ratio is often cited as about four males for every one female diagnosed. Other research indicates that it is closer to 3:1 or 2:1. One in every 42 males and one in 189 females in the United States is diagnosed with autism spectrum disorder. There is some evidence that females may also receive diagnoses somewhat later than males; however, thus far results have been contradictory. Men and boys tend to have higher rates of autism diagnosis, existing literature suggests that this can be attributed to the diagnostic frameworks which are based around men’s behaviours and symptoms rather than reflecting the likelihood of having autism based on biological sex or gender. Current research highlights that current diagnostic tools for ASD have been shaped by men and boys' behaviours and symptoms and has indicated a significant implicit gender bias towards associating males with autistic traits. This is consistent with having a higher male-to-female autism ratio and it supports the view that females are under-diagnosed or diagnosed later in life. This brings up the notion of whether autism is perceived as a male condition and disregards females with autism. Delayed diagnosis in women and girls can be attributed to socio-cultural expectations which induces camouflaging or “masking” strategies to present behaviours that are more societally acceptable. Moreover, gendered socialisation influences such strategies and affects how girls and women express autism, whereby, girls are expected to have caring, social and empathic characteristics before exhibiting behaviours that are more commonly associated with autism, such as aggressiveness and unresponsiveness. This conceals underlying autism symptoms due to differences in perceiving such traits in girls and boys.
Background
Hans Asperger was one of the first people to study autism, with all of his four study subjects being male. Another early researcher, Leo Kanner, described "autistic disturbances of affective contact" in the group consisting of eight boys and three girls. Autism Spectrum Disorder is commonly defined as a neurological developmental disorder with symptoms of poor social communication, repetitive behaviors, sensory sensitivities, executive dysfunction, and hyper-fixations. Women are less likely to be diagnosed as autistic than men; they are often misdiagnosed or not noticed to be neurodivergent by doctors. Women are also more likely to be diagnosed as autistic at a later age than men. There are many theories to explain this discrepancy in diagnoses, the most prominent being extreme male brain theory, imprinted brain theory, female protective effect theory, and female autism phenotype theory.
Theories explaining gender diagnosis disparity
Extreme male brain theory
Extreme male brain theory is an extension of the empathizing-systemizing theory, which categorizes people into 5 different groups based on their empathizing and systemizing expressions. In the general neurotypical population, females have a greater ability to empathize, and males have a greater ability to systemize. Simon Baron-Cohen's extreme male brain theory states that autistic males have higher doses of prenatal testosterone and on average have a more systemizing brain, as opposed to the more empathizing female brain. He suggests that autistic brains show an exaggeration of the features associated with male brains. These are mainly size and connectivity, with males generally having a larger brain, which is seen in an exaggerated form in those with ASD. Individuals with ASD were found to have widespread abnormalities in interconnectivity and general functioning in specific brain regions. This could explain the different results on empathy tests between men and women as well as the deficiencies in empathy seen in ASD, as empathy requires several brain regions to be activated which need information from many different areas of the brain. Baron-Cohen therefore argues that genetic factors play a role in autism prevalence and that children with technically minded parents are more likely to be diagnosed with autism. Although autistic females have been documented to have higher testosterone levels, which could support the extreme male brain theory, not all autistic females show male-specific symptoms, leaving the extreme male brain theory with Autism Spectrum Disorder to be controversial.
Imprinted brain theory
The imprinted brain theory suggests genomic imprinting is at least partly responsible for the sex differences in autism and implicates schizophrenia as well, claiming that genetic and physiological evidence suggests the two conditions are on a spectrum in which some mutations in certain genes cause lower social cognition but higher practical cognition (autism) while other mutations in the same genes cause lower practical cognition with higher social cognition (schizophrenia).
Female protective effect theory According to the female protective effect hypothesis, more genetic mutations are required for a girl to develop autism than for a boy. In 2012, Harvard researchers published findings suggesting that, on average, more genetic and environmental risk factors are required for girls to develop autism, compared to boys. The researchers analyzed DNA samples of nearly 800 families affected by autism and nearly 16,000 individuals with a variety of neurodevelopmental disorders. They looked for various types of gene mutations. Overall, they found that females diagnosed with autism or another neurodevelopmental disorder had a greater number of harmful mutations throughout the genome than did males with the same disorders. Women with an extra X chromosome, 47,XXX or triple X syndrome, have autism-like social impairments in 32% of cases.
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