From Our 2010 Archives
Autism Risk Rises With Mother's Age
The Older the Mother, the Higher Her Child's Autism Risk
Daniel J. DeNoon
Reviewed By Louise Chang, MD
Feb. 8, 2010 -- The older a mother is when she gives birth, the higher her child's risk of autism, new data show.
A smaller effect also is seen for the age of the father, but only when the child is born to a father over age 40 and a mother under age 30.
The new findings come from a comparison of reported autism cases in California to state singleton birth records from 1990 to 1999. Over that time, there were about 5 million births and more than 12,000 autism cases.
It's tempting to think that the trend for women to delay childbirth is behind the continuing rise of autism. But that's not the case. This trend accounts for less than 5% of the autism increase in California over the decade 1990-1999, calculate study researchers Janie F. Shelton, Daniel J. Tancredi, PhD, and Irva Hertz-Piccioto, PhD.
So what's going on? That isn't clear. Older parents' genes can undergo changes caused by aging and by the environment.
"We need to understand biologically why this is happening," Shelton tells WebMD. "It would be premature to tell older moms not to have a child. It could be the risk is associated with an exposure, and avoiding the exposure would be more important than not having kids at age 40."
Exactly what is a woman's risk of having a child with autism? The figures from the study come from 1990 to 1999. Autism cases increased throughout that decade -- and throughout the next decade, too.
"By now the rates are much higher," Hertz-Piccioto tells WebMD via email. She also notes that the cases counted in the study are only those receiving services from the state of California,- so the risks she and her colleagues calculate are underestimates.
From 1990 to 1999, the risk of having a child with autism was:
It's clear that a parent's age is only part of the autism puzzle, notes Geraldine Dawson, PhD, chief science officer for Autism Speaks, a group that advocates for autism research.
"This study does not say advanced mother or father age causes autism," Dawson tells WebMD. "This is one risk factor among many factors that contribute. In the majority of cases, we are not going to find that any one factor accounts for any individual child's autism. Parental age is just one risk factor that is interacting with other genetic and environmental factors that lead to a child developing autism."
The Shelton paper was in the Feb. 8 online advance issue of the journal Autism Research.
SOURCES: Shelton, J.F. Autism Research, published online Feb. 8, 2010.
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