Swedish researchers found out that autism risk in children grows as the fathers get older and even accelerates when the mothers are aged over 30 years.

A new study from the School of Public Health, Drexel University in Philadelphia in partnership with Karolinska Institute in Sweden shows more findings about the risk of conceiving a child with intellectual disability and autism spectrum disorder (ASD), associating it with the age of the parents.

According to the study that was published in the International Journal of Epidemiology Feb. 2014 issue, the advancing ages of mothers and fathers have different effects on the child's risk of autism. The increase in risk was larger for older mothers than to older fathers.

The risk of conceiving a child with autism in men increased linearly with age while women had a more complex relationship to the risk. Women who give birth to children with ASD before age 30 showed no association with age. The risk was very low. However, mothers who give birth at the age of 30 and above showed greater chance of developing ASD.

The maternal age effect is stronger than the paternal one and multiple mechanisms such as environmental risk aspects and pregnancy complications could account for the various patterns of risk. The steady increase with the fathers' ages is coherent to the hypothesis of increase genome changes over the father's lifespan and this can increase the ASD risk.

"The open question at hand really is, what biological mechanisms underlie these age effects?" senior author of the study Brian Lee, PhD said. "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 even though much recent discussion has focused on fathers' and even grandfathers' ages." Lee is an assistant professor in Drexel University School of Public Health and researcher at A.J. Drexel Autism Institute.

Researchers analyzed 417,303 Swedish children born between the years 1984 and 2003. Factors analyzed vary from influence risk and paternal age, each parent's psychiatric history and family income. "When considering risk factors, we can't necessarily lump all ASD cases together, even though they fall under a broad umbrella of autism," said Lee. "We need to keep an open mind in case intellectual disability might be a marker of a different underlying mechanism."

Lee also noted that the absolute ASD risk is around 1 in 100 in all of the samples and even less than 2 in 100 for mothers aged 45 years.

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