In somewhere between 74% and 98% of autism spectrum disorder cases, genes are to blame. So say researchers out of King's College London in the journal JAMA Psychiatry after studying both identical and fraternal twins. In fact, hundreds of genes could contribute to the development of autism, although because genes interact with the environment, that doesn't totally preclude the possibility that environmental factors are at play as well. "Our findings suggest environmental factors are smaller, which is important because some parents are concerned whether things like high pollution might be causing autism," one researcher tells the BBC. "The main consensus now is that the rise in diagnosis has more to do with increased awareness of the condition."
For the study, researchers used data from the population-based "Twins Early Development Study," looking at twins born in England and Wales between 1994 and 1996. Out of more than 6,000 initial sets of twins, home evaluations were performed on 516 twins, with 181 of the teenagers diagnosed with some form of autism, reports Health Canal. It turns out that the rate of autism was far higher among identical twins, who share identical DNA. (In each pair, both twins were raised by their parents in the same household.) The researchers are careful to note that the causes of autism remain unclear, and that researchers are now studying which genes contribute and how. (Earlier this year, researchers attributed the soaring rates of autism diagnosis to better awareness, not environmental factors.)