Industry statistics suggest that autism spectrum disorders (ASD) currently affect four times as many males as females. Now there are further clues as to why this disparity exists.
Research conducted by the Centre for Addiction and Mental Health (CAMH) and The Hospital for Sick Children (SickKids) revealed that specific alterations of DNA on the sole X chromosome carried by males contributes to a greater risk for the development of ASD.
The study was led by Dr. John B. Vincent, senior scientist and head of CAMH’s Molecular Neuropsychiatry and Development Laboratory in Toronto and Dr. Stephen Scherer, senior scientist and director of The Centre for Applied Genomics at SickKids.
An analysis was completed of the gene sequences of 2,000 individuals diagnosed with ASD alongside another group with intellectual disabilities. The results were then compared to thousands of population controls. Results indicated that mutations were present in the PTCHD1 gene on the X chromosome in one percent of the males with autism spectrum disorders.
In other male controls, similar mutations were not present, and sisters carrying the same mutation were not affected.
“We believe that the PTCHD1 gene has a role in a neurobiological pathway that delivers information to cells during brain development — this specific mutation may disrupt crucial developmental processes, contributing to the onset of autism,” said Vincent.
“Our discovery will facilitate early detection, which will, in turn, increase the likelihood of successful interventions.”
Scherer noted that ASD’s gender bias towards males has intrigued the scientific community for a number of years, and these findings may begin to offer an explanation.
“Boys are boys because they inherit one X chromosome from their mother and one Y chromosome from their father. If a boy’s X chromosome is missing the PTCHD1 gene or other nearby DNA sequences, they will be at high risk of developing ASD or intellectual disability.
Girls are different in that, even if they are missing one PTCHD1 gene, by nature they always carry a second X chromosome, shielding them from ASD,” Scherer adds. “While these women are protected, autism could appear in future generations of boys in their families.”
Autism spectrum disorders (ASD) are a set of neurological disorders that affect brain functioning, resulting in challenges with communication and social interaction, unusual patterns of behavior, and often, intellectual deficits.
It is estimated to affect one in every 120 children and specifically, one in 70 boys. Though all of the causes of ASD are not yet known, research has increasingly pointed toward genetic factors.
The research is published in the September 15 issue of Science Translational Medicine.