New research indicates that between 74% to 98% of autism spectrum disorder (ASD) cases are genetic in origin, according to a study published in JAMA Psychiatry.
A study of twins found that rates of autism were higher among identical twins compared with fraternal twins, which suggests that the condition is much more heritable than previously believed.
The researchers studied 516 sets of twins from the Twins Early Development Study (TEDS), which included twins raised in the same household by the same parents.
The researchers included twins regardless of their diagnosis of autism, which allowed them to assess the prevalence of autistic skills and behaviors as well.
“The novel aspect of this study was the inclusion of twins regardless of whether they had a clinical diagnosis,” said researcher Patrick Bolton, PhD, FRCPsych, of King’s College London, United Kingdom, in a statement. “This enabled us to get a more accurate picture of how influential a child's environmental experiences and their genetic make-up is on ASD, as well as on subtler expressions of autistic skills and behaviors.”
Autism has become much more prevalent in recent decades, and the researchers believe that it is an increased awareness of the condition that has contributed to that. Previously, many cases of ASD had been incorrectly classified as learning disabilities instead of autism.
Despite their findings and use of twins, the researchers noted that environmental factors could not be completely ruled out. However, the results do suggest that environmental factors are much less influential than genetics.