April 15 (UPI) -- Children born to parents 40 and older are around 50 percent more likely to be diagnosed with autism spectrum disorder than those whose mothers and fathers are between 25 and 29, a new analysis suggests.
Risk for ASD in children is up to 10 percent higher when their mothers or fathers are in their 30s, and more than 50 percent higher when mothers are in their 40s and fathers are in their 50s, according to the study, published in JAMA Network Open.
The risk factors for are all in comparison to when both parents were in their late 20s.
"Although the association between advanced maternal and paternal age at childbirth and risk for ASD in the offspring is rather robust and observed in several populations, scientists are still trying to understand what are the mechanisms that might explain these associations," Dr. Zeyan Liew, assistant professor of environmental health sciences at the Yale University School of Public Health, told UPI.
"It is also important to find out whether there any other modifiable risk factors that are correlated with age of delivery that we could address to help to mitigate the risk for ASD in the offspring of very young or older parents," he added.
An estimated one of every 54 children born in the United States has ASD, according to the U.S. Centers for Disease Control and Prevention, and research suggests that the numbers are growing. Earlier studies have also linked later parental age with increased risk for the disorder.
What's unique about the study by Liew and his colleagues, however, is that their analysis looked at multiple generations, taking into account the possible links between ASD and the age of grandparents as well as parents.
The team used data from Danish national health registries on nearly 1.5 children born between 1990 and 2013 and more than 350,000 fathers and more than 450,000 mothers born between 1973 and 1990. Among the children, more than 27,000, or roughly 2 percent, had ASD. The study included nearly 9,400 grandchildren with ASD.
In addition to increased risk for ASD among children born to parents of certain ages, the multi-generational analysis revealed that risk for the condition was 68 percent higher among grandchildren of maternal grandmothers and 50 percent higher among grandchildren of maternal grandfathers who were 19 years of age or younger at the time of giving birth to the parents. This is compared with the grandchildren of grandparents who were between 25 and 29 years old at the time of giving birth to the parents.
Risk was also 18 percent higher among grandchildren of younger paternal grandmothers and 40 percent higher among grandchildren of paternal grandmothers 40 years of age and older at the time of giving birth to the parents.
"Our findings of grandparents age at the time of the birth of the parents and future risk in ASD in the grandchild is novel, suggesting that possible transmission of ASD risk across generations should also be considered in future etiological research on ASD," Liew said.