Autism in some boys linked to missing DNA
Wed Sep 15, 3:54 PM
By Sheryl Ubelacker, Health Reporter, The Canadian Press
TORONTO - Researchers are a step closer to understanding why autism spectrum disorder affects four times as many boys as girls. A study led by a team of Toronto scientists has discovered that males who carry specific genetic alterations on their X-chromosome have an elevated risk for developing autism spectrum disorder, or ASD. “The male gender bias in autism has intrigued us for years and now we have an indicator that starts to explain why this may be,” said co-principal investigator Stephen Scherer, director of the Centre for Applied Genomics at Toronto's Hospital for Sick Children. The researchers, whose work is published this week in the journal Science Translational Medicine, found that about one per cent of boys with ASD had mutations related to the PTCHD1 gene on the X-chromosome. "Hearing that it's in one per cent doesn't get a lot of people excited," conceded Scherer. "But it gets geneticists really excited because there's a lot of genes involved (in ASD)." Boys inherit one X-chromosome from their mother and one Y-chromosome from their father, explained Scherer. "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. While these women are protected, autism could appear in future generations of boys in their families." ASD affects one in every 120 children — including one in 70 boys. The neurological disorder ranges in severity, but can cause difficulties with communication and interaction with others, unusual patterns of behaviour and intellectual disability. An estimated 190,000 Canadians have the disorder, which is on the rise worldwide, says Autism Society Canada. The isolation of genetic alterations on the X-chromosome within a percentage of individuals with autism follows a number of recent genetic discoveries by Scherer and others that are moving science slowly but surely towards a better understanding of the causes of the baffling disorder. To conduct this study, researchers analyzed the gene sequences of 2,000 individuals with ASD, along with others with an intellectual disability, and compared the results to DNA sequencing for thousands of healthy control subjects. While the PTCHD1 mutation occurred in one per cent of males with ASD, it was not present in the DNA of thousands of healthy male controls — and sisters of affected males carrying the same mutation seemed unaffected. "I don't think it's too surprising that there is another gene on the X-chromosome that is involved in autism," said co-principal researcher John Vincent, head of the molecular neuropsychiatry and development lab at the Centre for Addiction and Mental Health. "It's another one in the list and I think it will be one of the most common ones, so parents will be able to have their children tested," said Vincent. "Particularly if they have a son affected, it will be important for them to know if it's caused by a mutation at or around PTCHD1." "And if it is, they'll know that future (male) children would be at risk." The scientists believe the PTCHD1 gene has a role in a neurobiological pathway that delivers information to cells during brain development, and this specific mutation could disrupt crucial processes and contribute to the onset of autism, said Vincent. Having a test for the genetic mutation would mean children could be diagnosed at a younger age, allowing behavioural therapies to be started sooner, he said. "So the earlier you can catch it, the more effective the therapies can be."
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