A large new international study suggests the link between parental age and autism risk is more complicated than we knew.
While previous research has shown that advanced maternal and paternal age may play a role in the development of the disorder, this new study found that not only older mothers and fathers, but also teenage mothers and couples with large age gaps seem to be at a higher risk for having children with autism spectrum disorder, or ASD.
Researchers from universities in nine countries analyzed data from more than 5.7 million children in Australia, Norway, Denmark, Israel and Sweden -- the largest-ever data set for research into autism's risk factors. Of that group, 30,000 had ASD.
"The true impact of this study is not simply that we have confirmed parental age as a risk factor for autism," Dr. Michael Rosanoff, director of public health research at Autism Speaks, the organization that funded the research, said in an email to The Huffington Post. "It is that we have created an immense, multinational database that will allow us to continue to uncover environmental risk factors for autism."
Here are some of the most important findings from the new study:
- Dads over the age of 50 were 66 percent more likely than dads in their 20s to have children with autism, while dads in their 40s were 28 percent more likely.
- Teen mothers were 18 percent more likely to have children with autism than mothers in their 20s.
- Mothers in their 40s were 15 percent more likely to have children with autism than mothers in their 20s.
- Dads aged 35-44 who had an age gap of 10 years or more with their partners were also at a somewhat increased risk.
Scientists still aren't yet sure why both younger and older parental age seem to be risk factors.
"The mechanisms are unclear, but the likelihood and accumulation of genetic mutations in older parents’ sperm and egg cells are a possible explanation," Rosanoff said of the parental age association. "For teem moms, the explanation is even less apparent, as this is a new finding. One possibility is around suboptimal pregnancy among younger moms, who may have less access to prenatal care."
Of course, the researchers aren't sounding the alarm bells yet, and are careful to caution that there are many contributing factors for ASD, most of which are poorly understood.
“Although parental age is a risk factor for autism, it is important to remember that, overall, the majority of children born to older or younger parents will develop normally,” study co-author Dr. Sven Sandin, a medical epidemiologist at Mount Sinai and the Karolinska Institute, said in a statement.
Sandin also stressed that autism is relatively uncommon. "Autism is actually quite a rare disease, and I think that needs to be emphasized," he told Medscape News.
The study was published online last week in the journal Molecular Psychiatry.