Birgitta Steffensson1, Jan-Olov Larsson2, Ingegärd Fried2, Eman ElSayed2, Per-Anders Rydelius2, & Paul Lichtenstein1
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 was to evaluate whether genetic disposition for global maturity could be a mediator of the well-known findings of genetic factors for ADHD-symptoms.Through the population based Swedish Twin Registry, 1,480 pairs of twins aged 8-9 years were identified. A mailed questionnaire with items from DSM-III-R for ADHD and items concerning global maturity were completed by the parents. Genetic effects explained 68% of the variance in ADHD for girls, and 35% for boys. Global maturity mediated a portion of genetic effects for ADHD for both boys and girls. There were also shared environmental, as well as non-shared environmental effects unique to ADHD not in common with global maturity.The results show that there are at least two pathways in which genetic effects can influence ADHD; one through predisposition for maturational lag, indicating that maturational lag could be of importance for treatment and prognoses of ADHD, and one unique to ADHD, possible mediated by personality.
Address: Birgitta Steffensson, Division of Genetic Epidemiology, Institute of Environmental Medicine, Karolinska Institute, Box 210 S-171 77 Stockholm, Sweden. Telephone:+46-8-728 74 30. Telefax: +46-8-30 45 71. E-mail: Birgitta.Steffensson@imm.ki.se
1Division of Genetic Epidemiology, Institute of Environmental Medicine, The Karolinska Institute, Stockholm, Sweden. 2 Department of Child & Adolescent Psychiatry, The Karolinska Hospital, Stockholm, Sweden. 3Supported by the Swedish Society of Medicine.