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Studies Help Explain Why Autism is a Male Disorder

This week, a trio of articles were published in the journal Neuron on the genetics of autism.

One of the big take-aways is that there are likely to be hundreds of genes involved in creating the behaviors and symptoms that lead to an autism diagnosis — one study found 130 to 234 regions of DNA that were linked to autism, while another found 250 to 300.

That’s not a surprise (although some news headlines have made it sound like it is) — autism researchers have been aware of how genetically complex the disorder is for many years now.

The new piece that caught my eye had to do with how and why autism affects four times as many boys as it does girls. Apparently, the girls in the study had many more autism-associated genetic mutations than the boys — so why would boys be more likely to have the disorder in the end?

The average girl with an autism diagnosis had 15.5 genetic hiccups (called “copy number variants” — here’s an earlier article in my column explaining what this means) while boys on the autism spectrum had an average of two genes altered.

That means that, for whatever reason, the genetic tipping point for girls is much higher. Girls can have the same genetic alterations to genes but not have the disorder, whereas boys appear more vulnerable and will be affected by only a few changes to their genes. For a girl, it takes a “massive hit” to her brain networks to make a difference.

Why is that? Well, it’s not the first time we’ve heard that boys tend to be more vulnerable when it comes to health and development. But the researchers also wonder if sex hormones factor in, or if the X chromosome could be involved — boys only have one, so if there’s a genetic glitch on that one, it may have more impact.

Image: flickr

 

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