Autism: Is advance maternal age a true risk factor? New study suggests link.

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The newswires, blogs and tweets abound today with stories about a new study by the UC Davis M.I.N.D. Institute, which is reported to link advanced maternal age with increased risk of having a child with autism.  See the Institute’s Newsroom release on this study.                                            

The researches obtained the birth records for all births occurring in California from January 1, 1990 through December 31, 1999, which included demographics such as the parents’ ages.  Additionally, the researchers obtained the electronic records identifying children born during the study period who later received an autism diagnosis from the state Department of Developmental Services.  After certain exclusionary criteria were applied, the total study sample was approximately 4.9 million births during the study period of the 1990’s.  It was also determined that there were 12, 159 cases of autism, as that condition was defined “as a diagnosis of full-syndrome autism at a California Regional Center.”

The press release reports as follows:

The study found that the incremental risk of having a child with autism increased by 18 percent —  nearly one fifth — for every five-year increase in the mother’s age. A 40-year-old woman’s risk of having a child later diagnosed with autism was 50 percent greater than that of a woman between 25 and 29 years old.

Advanced parental age is a known risk factor for having a child with autism. However, previous research has shown contradictory results regarding whether it is the mother, the father or both who contribute most to the increased risk of autism. For example, one study reported that fathers over 40 were six times more likely than fathers under 30 to have a child with autism.

“This study challenges a current theory in autism epidemiology that identifies the father’s age as a key factor in increasing the risk of having a child with autism,” said Janie Shelton, the study’s lead author and a doctoral student in the UC Davis Department of Public Health Sciences. “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.”

Dr. Irva Hertz-Picciotto, a member of the Institute and the senior author of the report, in an interview with the Los Angeles Times said, “There is a long history of blaming parents for the development of autism.  We’re not saying this is the fault of mothers or fathers. We’re just saying this is a correlation that will direct research in the future.”

Another member of the research team, Janie E. Shelton, noted that while the data shows that the recent trend toward delayed childbearing contributed about a 4.6% increase in autism diagnoses over the decade –

Five percent is probably indicating that there is something besides maternal age going on because we are seeing a rise in every age group of parents.  We don’t know what the biology is. . . . We can’t say if it is age or something that is a proxy for age,” such as lifetime exposure to environmental pollutants, which accumulate in the body over the years.

The senior author, Hertz-Picciotto, added the following comment( as summarized by the LA Times reporter) for those who may prematurely  read too much into this report:

Older women are more likely to have problems with fertility and require intervention. They may be followed more closely during pregnancy, which would mean more ultrasounds. They are more likely to suffer gestational diabetes and to develop autoimmune disorders, which have been shown to play a role in autism. All are fertile areas for further research.

“We still have a real long way to go” in determining the causes of autism, she concluded.

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