Autism's higher prevalence in boys than in girls may be partly explained by a mutated gene located on the X chromosome, according to new research.
Earlier studies have found that mutations in the PTCHD1 gene, which plays a role in brain development in embryos, are a risk factor for autism spectrum disorders . Because the gene is found on the X chromosome, females have two copies of the gene, while males have only one.
Autism spectrum disorders affect a person's ability to communicate and interact with others and behave appropriately in social situations, according to the Centers for Disease Control and Prevention. They occur in 1 in every 110 children in the United States; they're found in 1 in 70 boys, and 1 in 315 girls.
In the study, scientists looked nearly at 2,250 people –– 2,000 of whom had an autism spectrum disorder and 246 who had other intellectual disabilities –– and 10,000 control individuals who didn't have autism.
They found the mutated gene in 1 percent of people with autism or intellectual disability –– almost all of whom were boys. The mutation was not found in any of the control subjects.
Because the mutation was relatively uncommon among boys with autism, it clearly cannot be said to cause the condition, according to the researchers. But because it was mainly found in boys, it may help explain the difference in the autism's prevalence between boys and girls.
"This finding begins to explain the sex bias we see in autism," Andy Shih, a scientist with the nonprofit group Autism Speaks, said in a statement. "Since males have one copy of the X chromosome while females have two, [males] have no 'backup copy'" if something goes wrong on the X chromosome.
In girls, the effects of the mutated gene may be covered by having a non-mutated copy of the gene on the other X chromosome.
But women who carry the gene could still pass it on to their children.
"While these women are protected, autism could appear in future generations of boys in their families," study researcher Dr. Stephen Scherer, director of the Hospital for Sick Children's Center for Applied Genomics in Toronto, said in a statement.
The study was published today (Sept. 15) in the journal Science Translational Medicine.