Numerous studies indicate that parental age is a risk factor for whether a child will develop autism spectrum disorder. Yet researchers have continued to question whether the mother’s age, the father’s age or both play a role.
Now, the largest study on parental age in autism to date confirms that kids born to older moms and dads do, in fact, have higher rates of autism. However, researchers found that teenage mothers are also at risk, along with parents who have a large gap between their ages.
The study, which was funded by the advocacy organization Autism Speaks and published June 9 in the journal Molecular Psychiatry, is based on data from more than 5.7 million children in five countries — including more than 30,000 with autism. The large sample size, researchers, say, provided them with more power than smaller studies to identify separate effects of maternal and paternal age.
In a way, the study’s findings validated what researchers already knew, says Brian Lee, an associate professor of epidemiology and biostatistics at Drexel University and a research fellow at the A.J. Drexel Autism Institute. “Parental age and autism has been linked … in different little samples here and there around the world,” says Lee, who was not involved with the research. “Not every single paper has found an association, but in general, the message seems to be that older parents face an increased risk of having a child with autism. This study — which is the most thorough and largest one that’s been conducted so far — confirms it.”
The overall chance that a child will be born with autism spectrum disorder is approximately 1 in 100. But the risk for autism was found to be 66 percent higher in children whose fathers were older than 50, versus kids whose fathers were in their 20s. And when it came to mothers, the study found that the autism rates were 15 percent higher in children whose mothers were in their 40s, compared to mothers in their 20s.
Experts believe the heightened risk of autism among older parents might be linked to genetic mutations in the sperm or egg cells. Other contributing factors could be environmental exposures, complications during pregnancy or the possibility that older parents might delay childbirth due to social reasons related to autism. “They may have autism characteristics, so it could be hereditary in that sense,” says study co-author Michael Rosanoff, Autism Speaks’ director of public health research.
The last hypothesis could explain why researchers saw an increased risk of autism among parents with disparate ages, Rosanoff says. Autism rates rose as the gap between two parents’ ages became greater. They peaked when fathers were ages 35 to 44 and their partners were at least 10 years younger, as well as when mothers were in their 30s and their partners were 10 years younger or more.
But the study also raised new questions, Rosanoff says, when it found autism rates to be 18 percent higher among children born to teenage mothers than among those with mothers in their 20s. “That hasn’t really been seen before, and we can’t really explain it,” he says.
One possible explanation, Lee suggests, is that younger moms may experience suboptimal pregnancies because they have less access to prenatal care — a hypothesis that warrants additional research.
Plus, important variables the study did not account for — but that could contribute to an increased risk of autism spectrum disorder associated with a young maternal age — are birth order and perinatal risk factors such as preterm birth and low birth weight, says Maureen Durkin, an epidemiologist and professor of population health sciences and pediatrics at the University of Wisconsin–Madison.
“Many studies find the risk of autism spectrum disorder to decline with increasing birth order. Birth order is correlated with maternal age, so it’s important to control for birth order when characterizing the impact of maternal age on autism risk. This study didn’t do that,” Durkin says. “The same can be said for preterm birth and low birth weight — risk factors for ASD that are also associated with teen pregnancy.”
Should older parents — or those with a 10-year or larger age gap — think twice before starting a family? Not necessarily, Durkin says. While parental age is one of many risk factors for autism spectrum disorder, the association is relatively weak.
“Most offspring of older parents do not develop autism — and the causal nature of the association is not fully understood,” Durkin says. “If a couple is faced with the decision of whether to delay childbearing until they finish school and are in a relatively stable position to provide parenting, or rush to have children when they are young to avoid autism, I would say the weight of the evidence favors the former approach.”
Experts also stress that although parental age is a risk factor for autism, it’s not the cause. And parental age doesn’t explain why some children develop autism and others don’t. “Not all older parents will have a child with autism, and not all children with autism were born to older parents,” Rosanoff says. “For us, it adds to the body of research around parental risk factors for autism; it seems that any risk factors are occurring around the pregnancy period, which seems to be a critical window.”
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Study: Parents’ Ages Linked to Autism Risk originally appeared on usnews.com
