Advances in genetic studies of attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (ADHD) is among the most common childhood-onset psychiatric disorders. Although family, twin, and adoption studies demonstrate that ADHD is a highly heritable condition, studies also suggest that genetic architecture is complex, prompting the use of more advanced methodologies such as genome-wide linkage and association studies. Although such studies are theoretically compelling, replication of these results has been inconsistent. Meta-analyses have produced more reliable results, but the associations identified to date account for only a small percentage of the genetic component of ADHD. Approaches such as neuroimaging genetics and epigenetic studies are being explored to probe further the etiologic complexity of this disorder.