The intergenerational recurrence risk of attention-deficit/hyperactivity disorder (ADHD) may be influenced by gender, and other psychiatric disorders may increase risk of ADHD in offspring, researchers found in a large study. Results were published in Journal of Child Psychology and Psychiatry.
Here, lead author and psychiatrist Berit Skretting Solberg, MD, PhD, of the University of Bergen, Norway, explains the reasons for the study, its key findings, possible clinical applications of the research, and her ongoing work in the field.
What led you and your colleagues to conduct this research?
I am a member of an attention-deficit/hyperactivity disorder (ADHD) research group led by Professor Jan Haavik in the Department of Biomedicine at the University of Bergen, Norway, recently a part of K.G. Jebsen Centre for Neuropsychiatric Disorders (2011-2018). The ADHD research group has collected phenotypic, imaging, and genetic data from a cohort of adults with ADHD (from 2004). The genetic data has been used in several larger studies, such as the genome-wide association studies conducted by Psychiatric Genomics Consortium.
This study is part of my PhD (supervised by Professor Kari Klungsøyr at the University of Bergen and defended February 2020), where the overall aim was to gain more knowledge about psychiatric comorbidity and heritability patterns in adults with ADHD using large Norwegian nationwide population-based registries. My work had a particular focus on sex differences in psychiatric comorbidity and transgenerational recurrence risks (from parent to child).
ADHD is a highly heritable neurodevelopmental disorder, but the intergenerational recurrence risk patterns of ADHD from parents to sons and daughters have not been studied, and we wanted to look into that.
Please briefly describe the study and its key findings.
We utilized a linkage of several unique, large nationwide population-based registries of more than 2.6 million individuals containing information about adults throughout their main reproductive period (15-45 years) with information about ADHD in offspring and parental psychiatric disorders available.
Our aim was to examine the recurrence risk of ADHD from mothers and fathers to offspring, and the risk of ADHD in offspring of parents with other psychiatric disorders, including an evaluation of the role of offspring sex.
We found that the prevalence of ADHD in offspring to affected parents was very high (17.8-24.2%), especially in sons (21.9-29.7%), and especially when both parents had ADHD, where 41.5% of sons and 25.1% of daughters had ADHD. We found a stronger recurrence risk of ADHD from mothers than from fathers, and in both cases, strongest to daughters.
Prevalence rates of ADHD were also higher in offspring to parents with certain other psychiatric disorders than in offspring of unaffected parents, but far lower than when parents had ADHD. We found that certain disorders in parents also confer increased risk of offspring ADHD, with parental sex-specific risk patterns, but with no differences between daughters and sons.
In line with the known heritability of ADHD, we have shown that parental ADHD has a strong, diagnosis-specific association with offspring ADHD.
Were any of the outcomes particularly surprising?
We were surprised by the very high relative risk of ADHD from mothers to offspring, especially to daughters, however, the absolute risk was higher to boys. We suggest some possible explanations including stronger maternal genetic effects, a stronger effect of maternal nontransmitted alleles (mothers’ behavior), the female protective effect (girls need greater exposure to genetic and environmental factors associated with ADHD to be diagnosed), and differences in health-seeking behavior (women seek health services to a larger degree than men).
We were also surprised by the similar risk estimates (~2.0) for ADHD in offspring of parents with other psychiatric disorders. We believe that shared common genetic and environmental factors between ADHD and other psychiatric disorders may contribute to this.
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