combinations of big-effect mutations and lots of different , smaller-effect ones could explain the wide spectrum of differences observed among autistic people . The evidence supports such a range , he says : everything from a few heavyhitting variations in some people , to an additive dose from many variants in others , and with overlap between the two patterns in still others . Geschwind adds yet another layer of complexity : the role of the cellular environment that all the other gene variants in a person create , known as the background effect . For example , someone could have a mutation conferring high risk that is either enhanced or diminished by the background input from other genes not
Scientists have identified many genetic variants that are linked to a raised risk of autism . Often , these variants affect the function of genes involved in the development and activity of brain cells . Here are four such genes , each of which carries instructions for a protein ( called MECP2 , PTEN , FMRP and SHANK3 ) that has an important function in neurons . Studies like this , of autism ’ s genetic causes , are teaching scientists more about brain biology .
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