Where do these new results leave us in terms of the root causes of autism? They certainly support the general idea that even sporadic cases of autism are caused by new mutations. But on their own, CNVs don’t seem to be occurring at a rate that is sufficient to account for all the sporadic cases of autism. There is the chance that many of the same genes we see within the CNVs, however, are damaged by smaller mutations, including single base changes, that can’t be detected by the techniques used in these studies. Identifying these sorts of mutations, however, will probably require whole-genome sequencing of thousands of individuals, so we’re unlikely to see it in the near future. The studies also leave open the possibility of environmental influences. Many mutations associated with autism show what’s called “variable penetrance,” meaning that they may affect some individuals severely, but leave others without any obvious or serious symptoms. The differences could be the product of environment, and will make identifying even inherited cases much more challenging. The second area where environment could come into play is the mutation rate itself. Many environmental factors can cause or promote the accumulation of DNA damage, which can produce the sorts of new mutations seen in these studies
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