Mothers diagnosed with attention deficit hyperactivity disorder (ADHD) are significantly more likely to have a child with an autism spectrum disorder (ASD), according to new findings from Florida State University. The study is the first of its kind of examine the inter-generational transmission of the two disorders in a large population. The research adds to the body of evidence about risk factors for autism.

Nearly one-third of children with ASD also meet the criteria for ADHD. The researchers engineered a study to determine whether the two conditions share genetic risk factors. They used a large dataset from Kaiser Permanente Northwest Health Plan, an insurance group that provides care for approximately half a million people in the Pacific Northwest. They selected electronic health records for children born from 1998 to 2004 to parents with Kaiser coverage who were still insured by Kaiser in 2012—a total of 43,030 children. Then, they sorted the children into those with ASD (609), with ADHD (213) or with neither disorder (27,770).

The analysis was restricted to only children and to the first-born children of multi-child families to prevent giving too much statistical weight to mothers with multiple children or older mothers, who are more likely to have children with autism. Of the mothers in the sample, 519 had a diagnosis of ADHD and a statistically insignificant nine mothers were diagnosed with autism.

When a mother is diagnosed with ADHD, the risk of having a child with autism increases by a factor of 2.5, even when controlled for the mother’s age, the child’s sex, and the age at diagnosis.

Researchers are not sure whether this constitutes a genetic risk, an environmental risk, or some combination of both. They say that the next step will be to undertake a similar study analyzing the ADHD-autism transmission from father to child, since men are more frequently diagnosed with both disorders.

This research is published in the Journal of Child Psychology and Psychiatry.

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