Medical investigators have come up with a possible explanation for the growing number of children being diagnosed with autism: Older parents are more likely to have a child who develops an autism spectrum disorder (ASD) than are younger parents, new research shows.
More parents are waiting to have children until they are in their 30s or older — years later than generations ago — and that trend could be contributing to the number of children born with the mental-health condition, the findings suggest.
"The open question at hand really is, what biological mechanisms underlie these age effects?" said Brian K. Lee, an assistant professor in the Drexel University School of Public Health who helped lead the study.
He added that the differences researchers observed in the ASD risks to children, based their mothers' and fathers' ages, spotlight a need to continue investigating underlying mechanisms of ASD.
The study — conducted in collaboration with the Karolinska Institute in Sweden and published in the International Journal of Epidemiology — analyzed the medical records of 417,303 children born in Sweden between 1984 and 2003.
Children born to mothers before the age of 30 were far less likely to develop autism, the results showed. But for babies born to mothers aged 30 and older, the chance of developing ASD rose rapidly with the mother's age.
The reasons for the increased risk are unclear, but the researchers suggested lifestyle and environmental risk factors occurring in women after age 30 could account for the differences. Complications in pregnancy, which rise with age, could also be a factor. But Lee said other factors may also be at work.
"When considering risk factors, we can’t necessarily lump all ASD cases together, even though they fall under a broad umbrella of autism," Lee said. "We need to keep an open mind in case intellectual disability might be a marker of a different underlying mechanism."
He added that the risks of having a child at an older age are still relatively modest. "The absolute risk of having a child with ASD is still approximately 1 in 100 in the overall sample, and less than 2 in 100 even for mothers up to age 45," he noted.
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