Why is Autism More Common In Males?

According to the American Journal of Human Genetics females require "more extreme genetic mutations than do males to push them over the diagnostic threshold for neurodevelopmental disorders". Sebastien Jaquemont of the University of Hospital of Luasanne suggests that "there is a different level of robustness in brain development and females seem to have the clear advantage." Some explanations for this have been indicative of there being a social bias that "increases the likelihood of diagnosis in males, whereas others have proposed that there are sex based differences in genetic susceptibility".
Jaquemont joined up with Evan Eichler of the University of Washington School of Medicine to go over DNA samples and data sets of some 16,000 people with neurodevelopmental disorders as well as 800 families being affected by ASD. The researchers looked over the CNVs, which are "individual variations in the number of copies of a particular gene--- and a single nucleotide variants (SNVs)---DNA sequence variations affecting a single nucleotide. Their results showed that females that had a neurodevelopmental disorder or had ASD, had a larger number of CNVs in comparison to their male counterparts, who had been diagnosed with the same disorder. In addition, females diagnosed with ASD had a larger number of SNVs than their male counterparts that had been diagnosed with ASD. The researchers came to the conclusion "that the female brain requires more extreme genetic alterations than does the male brain does to produce symptoms of neurodevelopmental disorder or ASD. Jaquemont summed up the results of his study by saying, "overall, females function a lot better than males with a similar mutation affecting brain development". He also said, "our findings may lead to the development of more sensitive, genetic-specific approaches for the diagnostic screening of neurodevelopmental disorders."
Dr. Lise Eliot talks about autism being a male trait in her book Pink Brain Blue Brain. Eliot writes that "autism is now one of the most prevalent syndromes of childhood" and that 80 percent of all kids diagnosed with autism are boys. Eliot goes on to say autistic children have "difficulty communicating, making eye contact and especially understanding that other people have thoughts and emotions different from their own. She goes on to say autistic children lack empathy and that because there are 3 to 4 boys diagnosed with the disorder to every girl with the disorder could mean that boys are more vulnerable because their brains innately lack circuitry for empathy."

Simon Baron -Cohen describes autism "as the consequence of an extreme male brain." Baron-Cohen thinks that prenatal testosterone is the cause for the child to develop autism. Baron-Cohen went on to say that "boys are exposed to higher testosterone levels in utero than girls are, and boys, as we've seen, show less eye contact, smaller vocabularies, lower empathy scores and more restricted interests. However, the prenatal testosterone correlation to autism is just a theory according to Baron-Cohen. A more likely logic for why males get autism compared to females is due to brain size. Baron-Cohen says the most definitive finding is, "the somewhat surprising overgrowth of the brain in the first year of life in children who are later diagnosed with autism. The brain is larger in autism (at least this is true during the first year of life) and boys have larger brains than girls do." This theory supports Baron-Cohen's "extreme male brain theory of autism".

Resources:

Eliot, Lise. Pink Brain, Blue Brain: How Small Differences Grow into Troublesome Gaps--and What We Can Do about It. Boston: Houghton Mifflin Harcourt, 2009. Print.

Cell Press. "Study uncovers why autism is more common in males." ScienceDaily. ScienceDaily, 28 February 2014. <www.sciencedaily.com/releases/2014/02/140227125236.htm>.