Genetic disposition for global maturity: An explanation for genetic effects on parental report on ADHD

Attention deficit hyperactivity disorder (ADHD) has been shown to be substa ntially influenced by genetic factors. However it is still not known how th ese effects are mediated. The aim of this study is to evaluate whether gene tic disposition for global maturity could be a mediator of the well-known f indings of genetic factors for ADHD symptoms. A total of 1480 pairs of twin s aged 8-9 years were identified through the population-based Swedish Twin Registry. A mailed questionnaire with items from DSM-III-R for ADHD and ite ms concerning global maturity were completed by the parents. The results sh owed that global maturity mediated part of genetic effects for ADHD for bot h boys and girls. There were also genetic, shared environmental, as well as nonshared environmental effects unique to ADHD not in common with global m aturity. Thus, there are at least two pathways through which genetic effect s can influence ADHD: one through predisposition for maturational lag and o ne unique to ADHD, possibly mediated by personality. The results indicate t hat maturational lag could be of importance for treatment and prognosis of ADHD.