Autism Risk Factors

New Studies Reveal Autism Risk Factors, First Common Gene Variants CME/CE
News Author: Janis Kelly
CME Author: Charles P. Vega

May 11, 2009 — New research shows that autism rates are higher for children who are firstborn or breech or whose mothers are 35 years old or older when they give birth. Further, 2 new genetics studies identify genetic abnormalities that affect 2 pathways involved in the formation of brain-cell connections.

Deborah A. Bilder, MD, and colleagues from the University of Utah School of Medicine, in Salt Lake City, found that having a child with autism-spectrum disorder (ASD) is 1.7 times more likely for mothers who give birth at 35 years or older compared with their women aged 20 to 34 years and 1.8 times more likely in the firstborn child. In addition, ASD children were more than twice as likely to have been a breech presentation.

"The findings of this study suggest that maternal age, parity, and breech presentation are independently associated with ASD risk. Additional investigations focused on both genetic and environmental factors that link these factors individually or collectively are necessary," the investigators write.

The study is published online April 27 in Pediatrics.

Results Warrant Careful Interpretation
Robert L. Hendren, DO, president of the American Academy of Child and Adolescent Psychiatry and an advisor to the Autism Society of America, told Medscape Psychiatry that clinicians should be prepared to reassure patients who might overinterpret the results of this study, despite the authors' careful presentation.

"Patients need to understand that association is not necessarily cause and effect," Dr. Hendren said. "Taken in conjunction with an earlier study that linked older fathers to increased ASD risk, this study suggests that there is some vulnerability factor associated with having older parents, but we have no idea what that might be. And older potential mothers certainly do not need to avoid having children because they are worried about this possible risk," said Dr. Hendren, who is also executive director of the MIND Institute and chief of child and adolescent psychiatry at the University of California, Davis.

Autism appears to develop from the interplay of a complex system of genetic and environmental factors. Previous research has suggested several prenatal, perinatal, and neonatal factors associated with a higher risk for autism, including advanced maternal and paternal age, a shorter length of gestation, low birth weight, meconium staining, hyperbilirubinemia, and breech presentation. In addition, parity may also affect the risk for autism. Research has most consistently demonstrated that the first child in the birth order has a higher risk for autism.

Previous research may have been limited by defining autism with only the most severe cases. The current study by Bilder and colleagues uses a broad definition of ASD and a very large control group from the same geographic area to further explore the issue of risk factors for autism.

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