Researchers from the Drexel University School of Public Health in Philadelphia and Karolinska Institute in Sweden provide more understanding on how the risk for autism is linked to parental age that varies between mothers and fathers age.
In this study, Dr. Brian K Lee, PhD, MHS, an assistant professor in the Drexel University School of Public Health and research fellow of the A.J. Drexel Autism Institute, and senior author of the study along with colleagues examined the independent and dependent associations of maternal and paternal age and risk of offspring autism spectrum disorders (ASD), with and without intellectual disability (ID).
The study looked at 417,303 Swedish children born 1984–2003. Among that number 4,746 children had autism. The study’s sample was obtained from national and regional registers. Researchers adjusted for numerous confounding factors that could vary with parental age and also influence risk, such as family income and each parent’s psychiatric history. The study also used a particularly comprehensive case-finding approach, to identify more ASD cases than other studies might, based on all pathways to care in a socialized health system.
The results showed in comparison to mothers at an average age of 29 years, mothers under 29 years had similar risks. The risk of autism increased after the age of 30 OR 1.75[95% (CI): 1.63–1.89] at ages 40–45. For fathers with an average age of 32 years, the odds ratio for ages 55–59 was 1.39 (1.29–1.50).
The risk of autism was greater for older mothers as compared with older fathers.
A goal was to study these parental age effects in more detail by looking at possible differing risks of ASD with and without intellectual disability; one of the most serious comorbid diagnoses with ASD, with a significant impact on functional status in life.
In their conclusion the researchers write” We confirm prior findings that advancing parental age increases risk of ASD, particularly for ASD with ID, in a manner dependent on co-parental age. Although recent attention has emphasized the effects of older fathers on ASD risk, an increase of n years in maternal age has greater implications for ASD risk than a similar increase in paternal age.”
The observed differences in risk based on mothers’ and fathers’ ages point to a need to continue investigating underlying mechanisms of ASD that may be influenced by a mother’s age, said Dr. Lee.
Dr. Lee comments “when considering risk factors, we can’t necessarily lump all ASD cases together, even though they fall under a broad umbrella of autism.” “We need to keep an open mind in case intellectual disability might be a marker of a different underlying mechanism.”
Dr. Lee noted whereas age effects are important indicators of risk at the population level that could eventually help researchers identify preventable causes of disability, they are not very significant for a couple’s family planning because the overall risk remains low.
“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,” comments Dr. Lee.
This was the first population-based study with an ASD sample large enough to study ASD risk in populations of children with and without intellectual disability.
This study is published in the International Journal of Epidemiology.