A recent study has found that most cases of autism appear to be associated with the appearance of new mutations that are not inherited from the parents.
According to researchers, risk-raising mutations, occurring in children but not their parents, were found in both protein-coding and regulatory genome regions.
These new mutations occur in regions of the genome that contain genes, which code for proteins, as well as in "non-coding" regions, which do not contain genes but which regulate gene activity, the researchers found.
Lead researcher Evan Eichler from the University of Washington said, "We are excited by these early findings because they suggest that multiple new mutations in a child, both coding and non-coding, are important to understand the genetics of the disease."
Although some forms of autism appear to run in families, most cases occur in families with no history of the disorder.
This form of autism, called simplex autism, is thought to occur from new mutations that first appear when the parents' sperm or eggs form.
These newly formed, or de novo, mutations are found in the affected child's genome, but not in either parent's genome. They are unlikely to occur in the affected child's siblings.
The team compared the genomes of 516 individuals, who had simplex autism with the genomes of their parents and one sibling who was not affected by the disorder.
By comparing these family members, the authors hope to identify new mutations that were more likely to appear in the affected child and more likely to be associated with an increased risk of developing autism.
They compared almost the entire genomes of the study participants, including the regions that do not include genes.
Although these "non-coding" regions do not include instructions for making proteins, they play an important role in regulating protein production by turning genes on and off and dialing their activity up or down.
The researchers observed that mutations that tended to appear in non-coding regions of the genomes occurred in areas known to influence gene activity in neurons located deep in the brain in a structure called the striatum.
This part of the brain is thought to play a role in some of autism behaviours.
Typically, the striatum coordinates planning, reward perception, motivation and other cognitive functions.
The findings suggest that relatively few of the new mutations in genes linked to autism risk were needed to increase the odds of having the disorder.
The research is published in journal Cell.
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