ADHD - An Illustrated historical overview

A family affair T he clustering of ADHD in certain families is a well known phenom- enon early described in the scientific literature. It has been discussed with regard to predisposing psychosocial family risk factors, genetic influenc- es as well as gene-environment and gene-gene interactions. Genes play a significant role as etio- logical factors of ADHD, and Kramer and Pollnow already mentioned a case of monozygotic twins with the core symptoms of ADHD in their seminal article. Initial family studies were later supplemented by adoption and twin studies showing a heritability that ex- plains on average about 80% of the phenotypic variance in the popula- tion (such as papers by the groups of Biederman, Faraone, Thapar and oth- ers). Molecular genetic studies indicate the multifocal genetic influence of a remarkable number of different gene loci distributed on different chromo- somes. Further genetic investigations reinforce the hypothesis that abnor- malities in the neurotransmitter sys- tem are a crucial predisposing factor, e.g. that there is an association with multiple transporter genes. Multigenerational family with high density of ADHD. Contributed by the Clinical Research Program CRU 125, University of Würzburg, Germany. ADHD subclinical symptoms no ADHD not known