Attention deficit hyperactivity disorder (ADHD) has been shown to be substantially influenced by genetic factors. However it is still not known how these effects are mediated. The aim of this study is to evaluate whether genetic disposition for global maturity could be a mediator of the well-known findings of genetic factors for ADHD symptoms. A total of 1480 pairs of twins 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 items concerning global maturity were completed by the parents. The results showed that global maturity mediated part of genetic effects for ADHD for both boys and girls. There were also genetic, shared environmental, as well as nonshared environmental effects unique to ADHD not in common with global maturity. Thus, there are at least two pathways through which genetic effects can influence ADHD: one through predisposition for maturational lag and one unique to ADHD, possibly mediated by personality. The results indicate that maturational lag could be of importance for treatment and prognosis of ADHD.

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The aim was to evaluate a questionnaire for parents concerning their school-aged children's global maturity level. Immature children (n = 29) as reported by their parents were compared to a control group (n = 68). Immaturity was linked to a reduced general knowledge, a childish body appearance, problems with the fine motor function and problems with peers. The index group also had on average a lower test result in total score of the Wechsler Intelligence Scale for Children and more commission errors in the Continuous Performance Test, both test results indicating a lower mental age.

The Gordon Diagnostic System (GDS) is a portable easily operated computerized tool developed to measure impulse control, attention and vigilance. In 1988, it was standardized for use among American children. The aim of this study was to evaluate the GDS for use among Swedish children. A clinical sample of 71 Swedish children, mean age 10.5 y, fulfilling the ADHD criteria according to the DSM‐IV was compared with a control sample of 88 children, mean age 10.2 y, with no known psychiatric diagnosis. The clinical sample showed lower GDS scores in all age groups, with some exceptions. The GDS scores were not associated with gender, but strongly associated with age, especially in the control sample. The accuracy of the GDS referring a specific child to either of the samples was, as expected, not impressive. With respect to the practical usefulness, the GDS was well accepted by the children and parents in both samples. The findings in age variation and when comparing children with ADHD and controls are in agreement with results from other studies.

We conclude that at least from the parents' point of view the behaviour problems in their children may be related to maturity.