Imagine you walked down the street and asked random people what autism is. What would they say? My guess: They’d talk about social skills, and the rising prevalence, and probably the vaccine nonsense. And they’d almost certainly mention that it happens to boys.

The idea that autism is a mostly male disorder is pervasive in the news, pop culture, and scientific circles. And it’s not just an academic curiosity. Last year a popular fertility clinic in Sydney, Australia, reported that about five percent of couples went through in vitro fertilization just so they could select a female embryo and thus lower the kid’s risk of developing autism.

The sex skew in autism is real: A diagnosis of autism is almost five times more common in 8-year-old boys than in 8-year-old girls, according to the latest statistics from the CDC.

But it’s not that simple. Most people don’t realize, for example, that autism’s sex bias changes dramatically depending on the severity of the disorder, with so-called high-functioning autism (a problematic term that usually means having an IQ above 70 or 80) showing a ratio more skewed towards boys. The ratio also varies wildly depending on who’s calculating it.

Two quick examples: A 2008 study of children in South Carolina found that among kids with IQs above 70, boys outnumbered girls 4.9 to 1. But among kids with IQs less than 70, the ratio was 2.4 to 1. And in the group of kids with the most intellectual impairments — IQs less than 34 — there were just as many girls as boys.

A 2010 study of children in the U.K. found the same trend but very different numbers. Among all children with autism, the male-female ratio was about 7 to 1, whereas among those with Asperger syndrome — characterized by high verbal and cognitive ability — it was 12 to 1.

I’ve just rattled off a bunch of numbers, and you might be wondering why you should care. But these numbers, as I learned this week, are powerfully charged.

Asking the question of why there’s a sex bias in autism brings up a host of messy social issues. Talking about autism’s sex ratio means talking about the challenges involved in diagnosing brain disorders, and the differences in the way we raise boys and girls, and possible differences between “male” and “female” brains, and the gender disparity in math and science fields.

It’s all so…uncomfortable. But I’m going to wade into the muck, anyway, with the hope of generating a meaningful and provocative discussion.

I’m thinking about all this now thanks to a paper published this week in the journal BioSocieties. In it, science historian Sarah Richardson of Harvard University and her colleague Eva Gillis-Buck argue that autism’s male bias has been greatly exaggerated. What’s more, they say, autism’s purported sex differences are often exploited by scientists outside of the autism field who want to take advantage of the recent influx of funding directed specifically at autism research.

And this whole situation, Richardson and Gillis-Buck worry, is not only bad for our understanding of autism, but is fueling unfounded cultural stereotypes. “Giving the gloss of scientific integrity to claims that autism is a disorder of gender I think contributes, mostly unintentionally, to negative stereotypes about women’s innate capacity for math and science,” Richardson says.

Some autism researchers take great umbrage at these claims. I’ll get to their rebuttal, but first I think it’s worth describing some of the intriguing historical context outlined in the new paper.

Extreme males

Boys took center stage in the first scientific reports of autism. Child psychiatrist Leo Kanner’s first description of the disorder, published in 1943, included 11 cases, 8 boys and 3 girls. In a later paper of 100 children Kanner reported a 4:1 male-female ratio.

Hans Asperger, who first described Asperger disorder in 1944, noticed it, too. “It is fascinating to note that the autistic children we have seen are almost exclusively boys,” he wrote. The reason, he explained, was in the difference between male and female intelligence:

“In general, girls are the better learners. They are more gifted for the concrete and the practical, and for tidy, methodical work. Boys, on the other hand, tend to have a gift for logical ability, abstraction, precise thinking and formulating, and for independent scientific investigation. …In general, abstraction is congenial to the male thought processes, while female thought processes draw more strongly on feelings and instincts. In the autistic person abstraction is so highly developed that the relationship to the concrete, to objects and to people has been largely lost.”

There was (and is) little evidence for this inherent distinction in male versus female thinking. (And as a side note, Asperger’s reasoning there assumes a very narrow conception of autism — you could say, after all, that many people with autism thrive on “tidy, methodical work”.)

Asperger was writing in a different era, of course, when these gender bifurcations were commonly accepted. But these ideas haven’t disappeared with modernity, thanks in large part to the work of psychologist Simon Baron-Cohen, one of today’s most famous autism scientists.

More than a decade ago, Baron-Cohen debuted a theory to explain the sex bias in autism. The so-called ‘extreme male brain’ theory says that autism’s primary characteristics are just an exaggeration of typical differences between men and women, and that they’re caused by excessive exposure to male sex hormones in the womb.

Baron-Cohen’s theory, as well as the methods of his studies that bolster it, have many scientific critics. (Cordelia Fine’s book, Delusions of Gender, gives a great overview.) And yet it has received an enormous amount of public attention. That’s partly because of how Baron-Cohen has trumpeted what he sees as its real-world implications.

The theory, he contends, explains many of the gender disparities between men and women. Take what he wrote in his 2003 book, The Essential Difference: “People with the female brain make the most wonderful counsellors, primary-school teachers, nurses, carers, therapists, social workers, mediators, group facilitators or personnel staff.”

Or this snippet from a column he wrote for the BBC in 2009:

“Males, maths and autism. On the face of it, these three things don’t appear to be linked. And yet they are. Males are much more likely to apply to university to study maths, for example. In 2007, three quarters of applicants to read maths at Cambridge were male, as were 90% of applicants for the computer sciences degree. Cambridge is not unique in this way. So why are males so attracted to studying maths? And why, in over 100 years of the existence of the Fields Medal, maths’ Nobel Prize, have none of the winners have ever been a woman?”

Why, indeed. Baron-Cohen’s column goes on to cite genetics and hormones. Unfortunately he makes no mention of the well-known social drivers of these gender differences.

There are many holes in the extreme male brain theory. To mention just one: Many studies have shown that people with Asperger’s aren’t particularly good at math and tend to have better verbal skills (a supposedly “female” trait). Based on my autism reporting over the past seven years I’d say the theory is not, by any stretch, a mainstream view among autism researchers. “On the other hand,” Richardson points out, “you see it cited everywhere.”

Funding for autism has skyrocketed over the last decade or so. In 2009, the National Institutes of Health spent $196 million on autism, compared with $186 million on Parkinson’s disease and $22 million on Down syndrome. In her new paper, Richardson takes a close look at hundreds of grant applications and published studies related to autism and sex differences. Many grant applications cite autism’s rising prevalence as prime motivation. But they also frequently site the sex bias and Baron-Cohen’s theory. Richardson describes grant proposals investigating autism’s sex bias through the lens of genetics, epigenetics, gene-hormone interactions, brain anatomy, chemical exposures, rat brain cells, and even the nervous system of worms.

She also found 442 studies related to autism and sex differences that have been published since 1980. Of these, 86 percent came out after 2001, and 10 percent were authored by Baron-Cohen. The rest came from laboratories in a variety of fields, including endocrinology, genetics, brain imaging, and molecular biology. Since 2001, animal research on this topic has exploded.

This is all evidence, Richardson says, that autism has become a “biomedical platform” for scientists of all stripes who are looking for funding, particularly in this era of shrinking science budgets.

“We show how, over time, researchers have begun to link their very basic research — even if it’s on nematodes — to frame it as a contribution to autism,” she says. “In the funding and publication structure, there’s been a real shift toward opportunistically using extreme-male-brain-type theories to gain research funding.”

Diagnostic dilemma

But is this a bad thing? I asked Richardson. Our society has evidently decided that autism is a pressing public health problem, and most of basic medical research is publicly funded. So isn’t it a good thing that all of these labs doing sex research are suddenly turning their attention to autism?

Richardson stresses that she is not arguing that sex difference research shouldn’t be done. But she does think it needs to be looked at with a more critical eye, particularly at the funding stage.

What’s more, she says, the growing obsession with autism’s sex bias is ultimately bad for our understanding of the disorder. “With this focus on the extreme-male-brain model,” she says, “you’re contributing to a kind of archetypal thinking about autism that obscures autism’s reality for many people.” It leads researchers to neglect boys with autism who don’t fit the math-geek stereotype, as well as girls with autism.

She makes a valid point there. Many autism researchers have decried the dearth of research on girls with autism, who tend to have a different symptomatic profile than boys do. That’s almost certainly due, at least in part, to differences in the way adults treat girls and boys. (One study, for example, found that mothers tend to talk more to young daughters than to their sons.) These gender differences in autism symptoms mean that many girls are missed by standard diagnostic tests. Even when symptoms are the same in boys and girls, it could be that parents, teachers and doctors don’t notice them in girls with a mild version of the disorder, but are primed to seek them out in boys.

Perhaps unsurprisingly, the autism scientists I contacted about this paper were not too happy about its claims.

They pointed out that many people studying sex differences in autism don’t accept the premises of the extreme male brain theory, and say it’s not relevant to the growing scientific interest in the disorder.

“The primary reason for funding in autism has nothing to do with sex differences in prevalence,” says Thomas Frazier of the Cleveland Clinic, who studies sex differences in children with autism. “It has to do with the massive functional impairment that most individuals experience, regardless of their sex or measured IQ.”

Lauren Weiss, a geneticist at the University of California, San Francisco, whole-heartedly agrees that autism scientists need to bring more girls into their research — she wrote a commentary about it for SFARI.org a few years back. But Weiss also says that Richardson puts too much emphasis on the extreme male brain theory, and doesn’t give enough credit to other studies suggesting that autism’s sex bias might indeed have biological underpinnings.

For instance, a genetic theory known as the ‘female protective effect’ says that girls carry some kind of (as yet mysterious) genetic variant that protects them from autism. In 2011, two studies found that among kids with autism, girls are more likely to carry genetic variants dubbed CNVs than boys are, and that the girls’ CNVs tend to be larger. This might mean that girls only get autism when their genomes take a major “hit”.

A study Weiss published earlier this year offers a different kind of genetic lead. She and her colleagues analyzed autism traits in people with four different genetic syndromes related to autism. These syndromes are all caused by a single gene, and none of them show a sex bias—girls are just as likely to have them as boys are. Intriguingly, though, Weiss found that for some of the syndromes, autism traits showed up differently in boys and girls, suggesting some kind of gene-sex interaction.

All that said, Weiss agrees that diagnostic bias may also play a role in autism’s sex skew. But the only way to tease apart cultural and biological factors, she says, is with more research on animal models and human patients.

“Just as evidence of biological genetic underpinnings helped to divert public opinion from the ‘refrigerator mother’ theory of autism etiology,” Weiss says, “scientists should encourage and not discourage biological understanding of sex differences that might be relevant to autism in order to refute any unfounded and damaging stereotypes about sex differences and in order to ensure that females as well as males with autism get appropriate care.”

A lot of the issues raised by Richardson’s paper may be obvious to autism researchers. But I do wonder about the general public. My sense is that when people hear (over and over again) about a sex bias in autism, their first thought is not about differences in the way the disorder presents itself in boys and girls, or about diagnostic biases. They think it means there must be an innate difference between boy brains and girls brains.

And perhaps there is. But the point is that nobody quite knows. If you come away with anything from this (very long!) post, I hope it’s this: Autism isn’t just a boy thing.

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