In addition to spontaneous mutations, environmental factors could play a part in non-hereditary autism cases, Smith said, explaining that unknown environmental factors, which older men have had more time to be exposed to, could promote genetic errors during sperm production.
Even though the rate of new mutations increases in children with age of the father, this should not be an argument for older men to avoid procreating or for younger men to freeze their sperm, Stefansson said.
"We don't know how large a percentage of cases of autism and schizophrenia are caused by de novo mutations," he explained. "The risk is not huge."
"On a grander scale, in the context of our species, the increasing mutation rate increases diversity when we are evolving," Stefansson said. "Getting rid of extra mutations might make us as a species less fit to survive the next natural disaster."
"This study should not be used as guidance for parents," Smith said. "Many cases of autism are from parents in their 20s."
For more about the signs and symptoms of autism, visit Autism Speaks.
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