A definitive cause for autism spectrum disorders (ASD) has remained elusive, although the best picture so far seems to be one of a mix of genetic and environmental factors. This suggests that any genes involved with the condition by necessity are being passed on from generation to generation. A new study now suggests that these genes are being positively selected for.
The study, published in PLOS Genetics, looked at the prevalence of alleles, or gene variants, commonly associated with an increased risk of ASD. The researchers discovered that these variants were found in much larger numbers than would be expected by chance, and they suggest that this may be because they are also linked to other genes implicated in cognitive ability.
The authors write that this positive selection between the genes thought to contribute to autism and those that might promote intelligence may explain why autism is such a prevalent condition, especially when it seems like it would have been selected against during human evolution.
“It might be difficult to imagine why the large number of gene variants that together give rise to traits like ASD are retained in human populations – why aren’t they just eliminated by evolution?” says co-author Joel Gelernter, professor of genetics and of neuroscience at Yale University, in a statement. “The idea is that during evolution these variants that have positive effects on cognitive function were selected, but at a cost – in this case an increased risk of autism spectrum disorders.”
The authors think that the positive relationship might be down to the fact that many of the gene variants found to be associated with ASD are also involved in molecular functions that affect the creation of new neurons. And so while conditions such as autism may be limiting to those who inherit genes that increase their risk for it, the genes are beneficial for our species as a whole as they may help in “intellectual achievement”.
The study is interesting as a possible explanation, or at least hint, as to why autism is so prevalent, but it still doesn’t fully explain the causes behind the condition. These gene variants are thought to increase a person's risk, but that means you could still carry them and not show signs of autism, and vice versa. It's a complicated condition and we still have a long way to go before we have a full explanation for it.
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