Until recently, autism without intellectual impairments, sometimes called Asperger syndrome, was thought to predominantly affect boys and men, at a ratio of 10 to every one woman.
However, there is growing evidence that the number of girls and women with the condition may have been vastly underestimated. Recent research, based on active screening rather than clinical or school records, found a ratio of 3:1. Happé and others believe this could fall further – potentially to as low as 2:1 – as diagnostic processes become better tailored to identifying autism in girls and women.
Due to early assumptions about autism mostly affecting men, studies have often recruited male-only cohorts. Male participants in brain imaging studies on autism outnumber females by eight to one, and in earlier research the bias was even more pronounced.
“This means that what we think we know about autism from research is actually just what we know about male autism,” said Happé, who has a £500,000 grant to investigate gender differences in autism spectrum disorders.
More recent work suggests there may be subtle differences in how autism presents in girls and women. Narrow special interests may superficially appear more mainstream (horses or boybands, say, rather than electricity pylons) – although the nature of the interest would still be unusual in terms of persistence and narrowness.
Autistic girls and women also tend to be more adept at masking their autistic traits. “They might pick a popular girl in their class or workplace and study them and copy them,” said Happé.
The idea that autism could be a result of having an “extreme male brain” due to hormone differences has dominated popular narratives about the biology driving the condition, although Happé said that the theory remained scientifically contentious. Media portrayals of autism, such as the movie Rain Man, have also been almost exclusively male. So parents, teachers and clinicians tend to be less inclined to consider autism as a likely explanation for girls and women struggling with social and communication problems than with boys and men.
The failure to diagnose autism is of concern because many of those affected experience secondary mental health issues such as anxiety, depression and self-harm. A small study last year found that 23% of women hospitalised for anorexia met the diagnostic criteria for autism. More work is needed to confirm the findings, which were based on 60 women, and to gauge whether the women’s social and communication difficulties predated their eating disorder.