In a study published in the May 2012 issue of the Journal of the American Academy of Child and Adolescent Psychiatry, led by Mr. Sven Sandin, of the Karolinska Institutet, Sweden and King's College London, researchers analyzed past studies to investigate possible associations between maternal age and autism. While much research has been done to identify potential genetic causes of autism, this analysis suggests that non-heritable and environmental factors may also play a role in children's risk for autism.

The researchers compared the risk of autism in different groups of material age (under 20, 24-29, 30-34, and 35+). They found that children of mothers older than 35 years had 30% increased risk for autism. Children of mothers under 20 had the lowest risk of developing autism. The association between advancing maternal age and risk for autism was stronger for male offspring and children diagnosed in more recent years.

The analysis included 25,687 cases of autism spectrum disorder and over 8.6 million control subjects, drawn from the 16 epidemiological papers that fit inclusion criteria for the study as defined by the investigators. The researchers identified and discussed several potential underlying causes of the association between maternal age and risk for autism such as increased occurrence of gene alteration during the aging process and the effects of exposure to environmental toxins over time.

Sandin said of the study, "The study makes us confident there is an increased risk for autism associated with older maternal age, even though we do not know what the mechanism is. It has been observed in high quality studies from different countries, including the US. All studies controlled for paternal age which is an independent risk factor for autism. This finding adds to the understanding that older age of the parents could have consequences to the health of their children."

This study was supported by the Beatrice and Samuel A. Seaver Foundation and Autism Speaks.