Roughly 3 to 5% of children with an aunt or uncle with autism can also be expected to have autism, compared to about 1.5% of children in the general population, according to a study funded by the National Institutes of Health.
Researchers found that a child whose mother has a sibling with autism is not significantly more likely to be affected by autism, compared to a child whose father has a sibling with autism. The findings call into question the female protective effect, a theory that females have a lower rate of autism than males because they have greater tolerance of autism risk factors.
The results, derived from records of nearly 850,000 Swedish children and their families, appear in Biological Psychiatry. The study was conducted by John N. Constantino, M.D., at Washington University in St. Louis, and colleagues in the United States and Sweden.
“The results offer important new information for counseling people who have a sibling with autism,” said Alice Kau, Ph.D., of the Intellectual and Developmental Disabilities Branch of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), which funded the study. “The findings also suggest that the greater prevalence of autism in males is likely not due to a female protective effect.”
One possible explanation is that females have a built-in resistance to the genetic factors leading to autism. With such a female protective effect, the theory holds that many women could carry such risk factors and be unaffected, but could transmit them to their sons, who lack the protective effect and may develop autism.
