Canadian researchers say they may have discovered part of the reason why autism spectrum disorder is four times more common in boys than girls.
Researchers from Toronto report in the journal Science Translational Medicine that a small percentage of boys with autism carry a gene mutation that's not seen in those without the condition.
The mutated gene is called PTCHD1 and is located on the X chromosome. Dr. John Vincent, who led the research and is the head of the Centre for Addiction and Mental Health (CAMH) Molecular Neuropsychiatry and Development Laboratory, says that since boys have only one X chromosome, they have no "backup " to make up for genetic variants.
"Any mutation in either X or Y is typically much more harmful," Vincent explained to CTV's Canada AM Thursday. "Girls are fortunate in that they have a second X chromosome so that a mutation in one can be compensated by the gene in the other X chromosome."
The PTCHD1 gene is thought to have a role in a pathway that delivers information to cells during brain development. When the gene is mutated, it can disrupt important developmental processes, leading to autism.
To find the mutation, Vincent's team examined the genes of almost 2,000 people with an autism spectrum disorder, along with 246 others with intellectual disability. They then compared the data to genes from more than 10,000 healthy individuals, who acted as a control group.
They found the PTCHD1 gene mutation in about one per cent of ASD-affected people in the study, but in none of the controls.
Vincent notes that although the mutation affects only a small percentage of boys with autism, every genetic discovery is important in understanding a complex condition like ASD.
"(Autism) is not like something like cystic fibrosis, which is a relatively straightforward disorder with just one main gene involved. We believe that in autism there are many, many genes contributing," he said.
"Each new gene is another step in the right direction, so even small progresses such as this are quite significant."
By next January, the research team hopes to have a test that will identify autistic boys with the mutation. That would allow any younger brothers to be tested at a young age.
As Vincent notes, spotting autism early in childhood is important.
"The key with autism is early intervention. So the earlier we can find the risk, the earlier we can implement therapeutic interventions," he said. "So having these genetic clues as early as possible will allow us to implement these therapies earlier."
An estimated 190,000 Canadians have autism spectrum disorder. It ranges in severity, but often includes problems communicating and interacting with others, as well as unusual patterns of behaviour.
