If you're a man, having children at an older age may put your grandchild at a higher risk of having an autism.
A new study, which was published in JAMA Psychiatry on March 20, found that risk factors for autism may increase over several generations.
"We tend to think in terms of the here and now when we talk about the effect of the environment on our genome," study co-author Dr. Avi Reichenberg, who worked on the study while he was at King's College London Institute of Psychiatry, said in a press release. He currently is at Icahn School of Medicine at Mount Sinai in New York. "For the first time in psychiatry, we show that your father's and grandfather's lifestyle choices can affect you."
Autism spectrum disorders are a group of developmental brain disorders that range in symptoms and severity, but almost always include social impairment, communication difficulties and repetitive and stereotyped behavior.
The Centers of Disease Control and Prevention announced on Wednesday that about 1 in 50 school children have autism, far surpassing the earlier estimate of 1 in 88. This means that at least 1 million children have the disorder in the U.S.
Researchers identified 5,936 individuals with autism and 30,923 healthy people born since 1932 using Swedish national registers.
They found that men who had a daughter when they were 50 or older were 1.79 times more likely to have a grandchild with autism than a man who had a child when he was 20 to 24 years old. Men who had a son at 50 or later were 1.67 times more likely to have a grandchild with autism.
"We know from previous studies that older paternal age is a risk factor for autism," lead author Emma Frans, from Karolinska Institutet, said in a press release. "This study goes beyond that and suggests that older grandpaternal age is also a risk factor for autism, suggesting that risk factors for autism can build up through generations."
The overall risk is small, and the study was only observational, meaning it did not prove that advanced age meant autistic grandchildren.
"Although there was a statistically significant increase in the incidence of autism in families with older grandparents, it must be remembered that autism was still extremely infrequent even in families with the oldest grandparents," Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven & Alexandra Cohen Children's Medical Center of New York, in New Hyde Park, said to HealthDay. He was not involved in the study. "Thus, older parents and grandparents should not be unduly worried."
Dr. Terry Brugha, professor of psychiatry at the University of Leicester who was not involved in the study, agreed.
"This is a solid piece of work and the findings are plausible. But as a grandparent or parent-to-be this is not something to be overly concerned about," she told the BBC. "We are at the early stages of research and this study gives us a slightly deeper understanding of what is going on in the background."