Boys diagnosed with autism far outnumber their female counterparts. Autism genetics researcher Ivan Iossifov lays out what research into the disorder’s genetic basis reveals about the reasons for this striking pattern.
Many of the numbers pegged to autism are staggering. By some estimates, as many as 1 in 68 children lies somewhere along the autism spectrum. Experts predict that as many as 500 or even 1,000 of the 20,000 genes in the human genome have the potential to contribute to autism if damaged. But perhaps the most baffling statistic is that a boy’s risk of autism is roughly quadruple that of a girl.
Scientists have yet to solve this mystery, but autism genetics researchers such as CSHL Assistant Professor Ivan Iossifov have uncovered some clues.
Certain genes that all humans have are particularly likely to contribute to autism if damaged. Iossifov and his colleagues have identified over 200 of these autism “risk genes” so far.
Autism’s bias against boys is a key element of the “unified theory of autism” that Iossifov’s colleague, CSHL Professor Michael Wigler, proposed in 2007. So far, the evidence has supported Wigler’s thesis that girls are to some degree protected from the effects of damaging genetic mutations.
Iossifov notes that, based on research he, Wigler and other colleagues have conducted in recent years, “When you look at girls, all the girls with autism have more, and more severe, damaging mutations compared to boys with autism.”
Boys and girls seem to have different thresholds for damage to autism risk genes. While boys with relatively little damage to autism risk genes may develop the disorder, girls typically only develop autism when they have mutations—sometimes in the same genes—that scientists describe as “devastating.”
This observation is just the beginning of the scientific journey to understand whether girls are in fact “protected” in some manner from some autism-causing mutations, and if so, what exactly protects them. One of the major factors in the way of this research, according to Iossifov, is that there are simply fewer girls with autism available to study. Advances in genetic sequencing techniques are helping to reduce this research barrier, however, by making genetic information more accessible.
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Note: For the sake of simplicity, this article uses the term ‘autism’ to refer to all autism spectrum disorders (ASDs). You can find out more about the distinction between autism and ASD here.
Ph.D., Columbia University, 2008