CBC News Posted: Apr 5, 2012 4:18 PM ET Last Updated: Apr 5, 2012 5:34 PM ET

A child is more likely to be born with autism if their father is over the age of 35 compared with a younger dad, new research suggests.

Researchers estimated that having a tiny, spontaneous genetic mutation boosts a child's risk of developing autism spectrum disorder between five to 20-fold.

Dr. Brian O'Roak studies genetic origins of intellectual,social and psychiatry disabilities in children at the University of Washington in Seattle. (Clare McLean)

"These results confirm that it’s not necessarily the size of a genetic anomaly that confers risk, but its location — specifically in biochemical pathways involved in brain development and neural connections," Dr. Thomas Insel, director of the U.S. National Institute of Mental Health (NIMH), said in his blog.

Three independent research teams made the genetic discoveries.

Evan Eichler and Dr. Brian O'Roak of the University of Washington in Seattle and their team found a mutation can happen with genetic material that comes from either parent, but it occurred four times more frequently in sperm cells than egg cells.

The older a father is, the more likely he is to have sperm with the spontaneous mutations, the researchers say.

Investigators analyzed DNA from 677 individuals from 209 families. From that, they identified 248 mutations of which 120 were classified as severe.

Each generation has on average one new coding mutation per child but not all cause developmental problems, the researchers said.

Like the larger deletions and duplications of genetic material that have previously been implicated in autism and schizophrenia, these newly discovered point mutations were part of the parents' DNA and became part of the affected child's.

The findings give scientists a road map to try to figure out how other genetic and environmental factors might influence autism, although they still don't know what causes the rare mutations or how common they are in the general population.

In this case, environment extends back to the time of conception, a potential trigger point.

"These studies begin to tell a more comprehensive story about the molecular underpinnings of autism that integrates previously disparate pieces of evidence," said Thomas Lehner, chief of NIMH’s genomics research branch, which funded the study by Mark Daly of Harvard University and MIT in Cambridge, Mass.

The studies were published in this week's issue of the journal Nature.

The U.S. National Institutes of Health funded one of the papers. Some of the study's authors had financial ties to the research.

http://www.cbc.ca/news/health/story/2012/04/05/autism-genetics.html