Genetic link ties ADHD risk to maternal age

Maternal age may be linked to prevalence of attention-deficit/hyperactivity disorder (ADHD), according to a new report. Whereas older mothers usually face more challenges, the study reveals that younger mothers may actually face a higher risk of having a child who develops ADHD.

The study, published in Scientific Reports, used the genetic data from more than 220,000 women in the United Kingdom, and found a strong association between a maternal age at first birth of 20 years or younger and ADHD in their children. The research team studied several genetic correlations to maternal reproductive traits, including age at first birth, age at first intercourse, age at first menstruation, age at menopause, and the number of live births. These traits were reviewed for correlation with 6 common psychiatric disorders in the children of these mothers, including ADHD, autism, bipolar disorder, depression, eating disorders, and schizophrenia.

Researchers also noted a positive association between polygenic risk scores and age at first birth with eating disorders, autism, and bipolar disorder, and linked ADHD polygenic risk scores to the mother's age at first sexual intercourse, her number of live births, and her age at menopause.

"In our study, there was no evidence that the risk of any psychiatric disorder modulated the phenotypes of the female reproductive traits. Therefore, the associations found in this study were mostly due to genetic pleiotropic effects," says Sang Hong Lee, PHD, associate professor at the University of South Australia School of Health Sciences and coauthor of the study. "Pleiotropy means that 1 gene influences 2 phenotypic traits like ADHD and age at first birth. By knowing such latent genetic mechanisms correctly, we may be able to better educate and support families in a near future. This is the context of precision health and medicine based on individual genetic characteristics, which is in its early stage.”

Lee says the research team was surprised overall at just how strong the correlation between young motherhood and ADHD risk was.

"During the course of the study, we found that the genetic correlation between ADHD and the reproductive trait was much higher than we thought," Lee says. "It was really interesting, and we tried to address the evolutionary hypothesis of positive association between ADHD and reproductive success. We were also excited to provide new findings that can have the potential to improve women's reproductive health."

Teenaged motherhood or young motherhood has already been associated with diverse effects on a child's mental health, Lee says, but the relationship between age at the initiation of motherhood and a child's mental health is complex. He says this study highlights the many factors that can play a role in a child's mental health history.

"This latent genetic mechanism should be carefully considered in infant mental clinical practice," Lee says. "Our findings can potentially help improve reproductive health in women and result in better child outcomes. For example, clinicians should consider the genetic predisposition of a young mother who may have the genes affecting ADHD risk, which is then inherited by her child."

Lee says this research is still in the early stages and more studies will be required to establish a genetic approach for how to possibly prevent ADHD in children in relation to young motherhood.