Back in the 1960’s a psychoanalyst called Bruno Bettelheim put forward the theory that autism was a result of faulty parenting. This view, which caused distress and stigma to generations of parents, has been comprehensively refuted by scientific research into the causes of autism, including studies showing that genetic factors play a major role in autism.
Autism often runs in families. In families with a child with an autism diagnosis, there is an increased chance that one or more siblings or parents may also be on the autism spectrum, or show some mild autistic traits.
Twin studies have provided convincing evidence that these family patterns are not due to faulty parenting, but due to genetic factors. Twin researchers compare sets of identical twins – twins who have exactly the same genetic information- with sets of non-identical twins – twins who share on average about 50% of their genes, just like ordinary brothers and sisters.
These studies have shown that where one twin of an identical pair has a diagnosis of autism, its highly likely (current estimates suggest between 60 - 95 %) that the other twin will also be on the autism spectrum. This risk is much lower for non-identical twins (0-30%) and for ordinary brothers and sisters (5-20%). This striking difference between identical twin and non-identical siblings, suggests that autism is strongly influenced by genetic factors, that is by particular gene variants which predispose an individual to autism.
Many research groups around the world are trying to elucidate which variants in the genetic material may be influential in predisposing people to autism. This quest is proving to be extremely difficult, as it is increasingly clear that there isn’t one single gene for autism. Rather, autism can be caused by a large number of different gene variants, and different genes may be linked to autism in different individuals or different families. These ‘risk genes’ can be inherited from the mother or father, which could explain familial forms of autism.
But recent studies suggest that new genetic changes that are not inherited from either parent, so-called de novo mutations, can also play a role in the development of autism. Researchers think that these de novo gene variants may play a more prominent role in those families where just one person has autism (also called sporadic autism). The occurrence of new genetic changes, not inherited from either parent, could explain why in some families only one person is affected by autism.
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