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Study reveals new piece in autism puzzle
An inherited mutation of a gene has been linked to the development of autism and intellectual disability in boys, an international team has found.

The study, reported today in Science Translational Medicine , shows mutations in the PTCHD1 (patched-related) gene are linked to the inheritance of autism and intellectual disability in a small number of cases.

Autism is a disorder that at its most severe can result in severe language and social impairment and is now included under the term 'autism spectrum disorder' (ASD), which also includes milder cases known as Asperger's syndrome.

There is no known underlying cause, although autism can often run in families, suggesting a genetic cause.

For the study, the researchers analysed the patched gene sequence from 1896 patients with ASD and 246 with intellectual disability.

The results were compared with those of more than 10,000 control individuals.

The team, led by Dr John Vincent, of Canada's Centre for Addiction and Mental Health , found mutations in various parts of the patched gene in 25 affected individuals (1% of patients) in 20 different families, but not in any of the controls.

Because the patched gene is located on the X chromosome, almost all of the affected patients were male, and most had unaffected mothers and other female relatives.

This means sons whose mothers carry a mutation at PTCHD1 may have a higher risk of developing ASD, the researchers say.

Dr Stephen Scherer, director of The Centre for Applied Genomics at SickKids, in Toronto, Canada, says the finding may help explain the male bias in autism, which affects four times as many males as females.

"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 says.

"While these women are protected, autism could appear in future generations of boys in their families."

The team also discovered that the patched gene is part of a neurobiological pathway called the Hedgehog signalling pathway, which gives cells information needed for the proper development of human embryos.

"This specific mutation may disrupt crucial developmental processes, contributing to the onset of autism." says Vincent.

"Our discovery will facilitate early detection, which will, in turn, increase the likelihood of successful interventions."
Autism puzzle

Study co-author, Professor Jozef Gecz of The Adelaide Centre for Neuroscience Research , says the paper adds another important gene to the autism puzzle and will help lead to a better understanding of the disorder.

The University of Adelaide researcher says it also adds to growing evidence that such genes alone might not be the only cause of intellectual disability and autism and that other genes in the genomes of these individuals may contribute.

Although the same gene may be at the root of the problem, the same mutation can generate different clinical outcomes in different individuals, says Gecz.

"Many [researchers] believe you have a mutation in the gene and you have a clear outcome.

"We see it slightly differently. The same gene may be at the root of the problem, but the same mutation can generate different outcomes in different individuals," says Gecz. "This is because of yet-to-be understood complex interactions with other genes and likely also environmental factors during development."

He says such variable clinical expressivity of even a single gene mutation does create complexity for genetic counselling of individuals at risk of having affected children because of the inability to predict the severity of the disorder accurately.

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