Why are boys four times more likely to have autism than are girls? We now have another clue, as investigators have discovered a gene mutation that puts boys at high risk of developing autism spectrum disorder (ASD).
Autism in Boys and the PTCHD1 Gene
Many researchers have been searching for reasons why autism affects more boys than girls. In 2007, the National Institutes of Health, along with several other organizations, reported that boys with autism and ASD had higher levels of hormones involved with growth when compared to boys who do not have autism.
In a University of California, Los Angeles, study published in 2009, investigators identified an autism-risk gene called CACNA1G, which is more common in boys than in girls, although why is not clear. CACNA1G is found on chromosome 17 and is responsible for regulating the flow of calcium into and out of cells. It is just one of several genes that have been linked to autism in previous studies, and now a research team has discovered yet another one.
The latest genetic link comes from experts from the Centre for Addiction and Mental Health (CAMH) and The Hospital for Sick Children. Scientists evaluated the gene sequences of 2,000 people who have ASD, as well as others who have an intellectual disability. These sequences were compared with thousands of controls.
One percent of boys with ASD had mutations in the PTCHD1 gene, which is on the X-chromosome. (Males are males because they inherit one X-chromosome from the mother and one Y-chromosome from the father. Girls inherit one X-chromosome from each parent.) None of the male controls had these mutations, and sisters of the affected boys who carried the same mutation did not appear to be affected.
Dr. Stephen Scherer, senior scientist and director of The Centre for Applied Genomics at SickKids, and director of the McLaughlin Centre at the University of Toronto, remarked that “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.” In girls, however, even if they do not have one PTCHD1 gene, their second X-chromosome can protect them from autism.
This newest discovery of a gene linked to autism in boys provides scientists with yet one more clue as to why the disorder is more prevalent in males than in females. Study leader Dr. John B. Vincent, senior scientist and head of CAMH’s Molecular Neuropsychiatry and Development Laboratory, added that “Our discovery will facilitate early detection, which will, in turn, increase the likelihood of successful interventions.”
Centre for Addiction and Mental Health news release, Sept. 16, 2010