In autism, the genetic causes are not as important as previously thought. In fact, they only explain half the risk, says a recent study. The environment does the rest.
The environment, as important as genes to explain autism. These unexpected results come from a large study carried out in Sweden, on 2 million people. Published in the Journal of the American Medical Association (JAMA) this May 3, a study relativizes the genetic causes of this neuro-developmental disorder.
Family and individual factors
Until now, genes have been estimated to account for 80-90% of the causes of autism. If the exact origin of this disorder is still not known, it turns out that the environment is more involved. 50% of risk factors are genetic, the rest are from the shared environment (family factors) or not shared (individual factors). Moreover, most often, the latter is the main source of environmental risk.
“We were surprised by the results, since we did not expect such an importance of environmental factors in autism. Recent research has focused on genes, but it is now clear that we need to further study and identify these environmental factors, ”says Prof. Avi Reichenberg, who led the study at King’s College London (UK). “Just as you have to look at many genetic factors, there are probably a wide variety of environmental factors that contribute to the development of autism. “
Autistic brother doubles risk for child
However, there is no question of abandoning the study of the genetic causes of autism. For the moment, two measures allow the risk to be assessed: heredity and the recurrent relative risk – which is defined according to family proximity to a person with autism. This is precisely what the second part of this study evaluates. Thus, having an autistic cousin doubles the risk of developing one, a half-brother or a half-sister three times. In children whose siblings have autism, this risk is increased tenfold.
These results provide a valuable tool for counseling parents with one child with autism who are considering having a second. “Our study was prompted by a question that parents often ask themselves: ‘I have a child with autism, what is the risk that my next child will be too?’ Our study shows that at an individual level, the risk of autism increases with proximity to an autistic parent, ”explains Dr. Sven Sandin, author of the study. “We can now provide reliable information about the risk of autism, which can reassure and guide parents and doctors in their decision-making. “
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