The heritability of any illness describes the genetic and environmental risk factors of that illness. Heritability for mental health issues can include family history, parental illness, exposure to maltreatment, and other factors that could increase vulnerability. Research on attention deficit hyperactivity (ADHD) has shown high levels of heritability in children. Children who have significant attention and hyperactivity issues often have a parent or sibling with ADHD. According to parent and teacher reports, the factors that put children at risk for ADHD are relatively similar across gender, race, age, and culture. But less is known about heritability of symptoms for adults with ADHD. It is estimated that over half of children who have ADHD will continue to have symptoms that persist into adulthood. This can present challenges for these adults across numerous domains, including careers, families, and interpersonal relationships. Therefore, Henrik Larsson of the Department of Medical Epidemiology and Biostatistics at the Karolinska Institutet in Sweden wanted to get a clearer picture of how heritability fluctuates from childhood to adulthood for people with ADHD.
Using a sample of 15,198 adult female and male twins with ADHD, Larsson evaluated self-reports detailing symptomology and genetic and environmental risk factors. He found that although symptoms appeared to decrease from childhood to adulthood for many of the participants, the symptoms were still present. Larsson found no differences between males and females with respect to heritability, but he did find that heritability decreased significantly in adulthood. Specifically, the levels of heritability that put the participants at risk were quite high in childhood, but much lower in adulthood. Larsson believes that several things might contribute to these discrepancies. First, when twins and siblings enter adulthood, they rarely share the same environment that they did as children. In childhood they are in the same home and witnessing the same things. In adulthood they may live apart and may be exposed to entirely different environmental experiences. “Another possible explanation for the observed discrepancy is that self-ratings for adult ADHD symptoms may have lower reliability compared to informant reports,” said Larsson. Therefore, the adults in this study may be minimizing symptom manifestation which could affect heritability. Overall, these findings show that even though there are still broad heritability factors for adults with ADHD, ratings of these factors may be distorted. Future work might consider using rater evaluations as a way to clarify these results.
Larsson, H., et al. (2013). Genetic and environmental influences on adult attention deficit hyperactivity disorder symptoms: A large Swedish population-based study of twins. Psychological Medicine 43.1: 197-207. ProQuest. Web.
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