Older Maternal Age Linked to Increased Risk for Autism in Children
By Caroline Cassels
Medscape Medical News
February 11, 2010 — Advanced maternal age significantly increases the risk of having a child with autism irrespective of paternal age, a large population-based study suggests.
The research, conducted by investigators at UC Davis Health System, Sacramento, California, shows that the incremental risk of having a child with autism increased by 18% for every 5-year increase in maternal age.
"These data show that the risk of having a child with full-syndrome autism increases with maternal age, but increased risk from advancing paternal age primarily occurs among younger mothers (<30)," the researchers, led by senior investigator Irva-Hertz-Picciotto, PhD, MPH, write.
According to lead study author Janie Shelton, a doctoral student, the study challenges the hypothesis that the father's age is a key factor in increasing autism risk.
"It shows that while maternal age consistently increases the risk of autism, the father's age only contributes an increased risk when the father is older and the mother is under 30 years old. Among mothers over 30, increases in the father's age do not appear to further increase the risk of autism," Ms. Shelton said in a statement.
The study was published online February 8 in Autism Research.
According to the study, previous research on autism and paternal age have yielded conflicting results on whether mothers, fathers, or both contribute to an increased risk for autism in children.
To determine the independent or dependent effect from each parent, the researchers gathered electronic records for all births in California between January 1, 1990, and December 31, 1999. The records incorporated detailed demographic information, including the age of both parents.
To identify which children would subsequently develop autism, the investigators obtained electronic records identifying children born during the study period who later received an autism diagnosis from California's Department of Developmental Services. For the study, autism was defined as a diagnosis of full-syndrome autism at a California regional center.
The final study sample included 4.9 million births and 12,159 cases of autism. The researchers report that for older mothers there was a stepwise progression in the risk of having a child who would later be diagnosed as having autism, irrespective of the father's age.
"We demonstrate that advancing maternal age increases the risk of autism independent of father's age, while advancing father's age increases the risk of autism primarily for mothers under 30. Among mothers over 30, we observed a small increased risk only among fathers 40+; even at the highest age group, the increase was smaller and less precise than that for fathers 30-34 among younger mothers," the researchers write.
At this point, the reason parental age influences autism risk is not clear. "We still need to figure out what it is about older parents that puts their children at greater risk for autism and other adverse outcomes, so we can begin to design interventions," Dr. Hertz-Picciotto said in a statement.
The study authors have disclosed no relevant financial relationships.
