The exact etiology of ADHD is unknown but is thought to involve structural and neurochemical alterations in brain regions responsible for executive function, memory, and information processing.[1][2] Norepinephrine and dopamine signaling play a major role in the function of these brain regions, and individuals with ADHD tend to have lower levels of both of these neurotransmitters than individuals without ADHD.[1]
ADHD has a strong genetic component. The risk of ADHD is increased by 2–8 times in individuals who have a parent or sibling with ADHD, and pooled twin studies suggest that the heritability of ADHD is nearly 80%.[3]