Genetics of attention-deficit/hyperactivity disorder: an update.

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder affecting children, adolescents, and adults. The prevalence is estimated at 5 to 7% of school-aged children and 2.5 to 5% of adults. The phenotype is complex and heterogeneous, presenting variable clinical features, developmental course, and outcome. The genetic susceptibility to ADHD is attributed to both common and rare variants from a broad range of genes related mainly to neurotransmission and neurodevelopment pathways. However, it has been difficult to identify the genetic risk variants that account for the high heritability of this disorder. In this paper, we present recent findings from molecular genetics studies on both child and adult ADHD. Challenges and future directions for ADHD genetic studies are reviewed and discussed.