A child’s environment exerts a strong influence on the severity of her autism, according to a study of 78 pairs of identical twins in which at least one twin has autism.
Researchers presented the unpublished results [January 16] at the 2019 International Society for Autism Research annual meeting in Montreal.
Studies in identical twins have shown that autism has a strong genetic basis: If one identical twin has autism, the other one has it, too, as much as 90 percent of the time.
The new work supports these estimates: In 64 of the 78 twin pairs, both twins have an autism diagnosis. However, autism severity often differs greatly within the twin pairs. In one twin pair, for example, one boy is essentially nonverbal, whereas the other has excellent speech.
“It’s almost impossible to believe that identical twins can be so different; it’s remarkable,” says lead researcher John Constantino.
The results suggest that the quality of life of autistic children is not hardwired by their genetics.
“The talk shows that the environment matters a lot, which to me is hopeful because it means that even if a child has a strong genetic burden, there’s a lot yet to be determined and room for improvement,” says [professor] Lucia Peixoto.