[img_inline align=”right” src=”http://padnws01.mcmaster.ca/images/Szatmari, Peter1.jpg” caption=”Dr. Peter Szatmari, director of the Offord Centre for Child Studies and head of the Division of Child Psychiatry at McMaster. File photo.”]

A Canadian team of researchers that includes McMaster's Dr. Peter Szatmari has taken another major step in unraveling the mysteries of autism with the discovery of numerous chromosomal regions containing genes that confer susceptibility to autism spectrum disorder (ASD).

Gains or losses of genes (referred to as copy number variation or CNV) were found in seven per cent of the 400 autistic individuals examined. In addition, a new region was identified on chromosome 16 which conferred risk of ASD in one per cent of families.

The results are published today in the American Journal of Human Genetics.

The study builds on the results the group published last February, in which genome-scanning methods were used to examine the genetic architecture underlying susceptibility to autism.

These discoveries are leading researchers closer to understanding the biochemical disruptions and pathways that lead to the development of ASD, said Szatmari, director of McMaster University's Offord Centre for Child Studies and head of its Division of Child Psychiatry.

“Our finding that in seven per cent of families we find chromosome changes in ASD children not seen in their parents has important clinical implications,” said Szatmari. “Our experience through this study indicates that application of these new microarray-based genome scanning tests may serve to focus clinical examination in a search for undetected syndromes leading to ASD.”

In addition to having potential clinical diagnostic importance, the findings further unlock the biological mysteries of why autism develops and what parts of the brain are involved. These advances can lead to better diagnostic tests, and eventually, more efficient treatments, said Szatmari.

Autism is a complex developmental disorder found in roughly one in 165 children, making it the most common form of any neurological disorder or severe developmental disability of childhood. Those

affected exhibit severe impairments in reciprocal social interaction and communication, and a preference for repetitive, stereotyped behaviours.

Structural changes along chromosomes have been previously identified in some individuals with ASD, but the full etiologic role of these is unknown.

Dr. Stephen Scherer, senior corresponding author on the study published today, and a senior scientist in Genetics and Genomic Biology at The Hospital for Sick Children in Toronto, said that in this phase of the group's work, newer microarrays were applied, allowing researchers to better scrutinize DNA for CNV changes in autism.

“We focused on Canadian families because of the detailed clinical information collected at McMaster and HSC over the years,” said Scherer, who is a professor of molecular genetics at the University of Toronto.

The team's findings about CNVs on chromosome 16 in one per cent of the Canadian cohort have also been described in American families in studies published last week in the New England Journal of Medicine and Human Molecular Genetics.