Attention deficit hyperactivity disorder (ADHD) is a prevalent, early onset and persistent, disorder of inattention, hyperactivity and impulsivity. The mechanisms of action of ADHD medications, neuroimaging studies and studies of monoamine systems and animal models suggest that dysregulation of catecholaminergic neurotransmission in cerebellar-corticostriatal circuits plays a key role in the pathophysiology of ADHD. The efficacy of ADHD medications likely arises from their differing profile of effects on a) dopaminergic and noradrenergic systems and b) the localization of these effects in prefrontal cortex and striatum ADHD has a very high heritability and although molecular genetic studies have found no causal common DNA variants yet, they have found strong evidence that rare duplications and deletions are risk factors for ADHD. Environmental risk factors, especially those that impact early neurodevelopment (i.e., exposure to cigarette smoking and alcohol during pregnancy), also influence susceptibility to ADHD.
Molecular genetic contribution to the developmental course of attention-deficit hyperactivity disorder