Genetic background of ADHD: population studies, genes of the catecholamine system

Attention-deficit hyperactivity disorder (ADHD) begins in early childhood. In this article we review the studies supporting a genetic background of this disorder. ADHD occurs in 3-10% of the general population. Family studies reveal a 5 times more likely frequency of ADHD among first-degree relatives than in the general population. Monozygotic twin concordance rate for ADHD is 81%, whereas for dizygotic twins it is 29%. One of the ADHD predisposing factors is dopaminergic neurotransmission abnormality. According to other studies there is a relationship between polymorphism of dopamine transporter gene (DAT), dopamine receptors genes: DRD2, DRD3, DRD4, DRD5, dopamine-beta-hydroxylase gene (DBH) and catechol-O-methyltransferase gene (COMT) and ADHD. In other articles authors describe abnormalities of the serotonergic system, such as the polymorphism of the serotonin transporter gene (5HTT/SERT), serotonin receptors genes 5HT2A and 5HT1B in the development ofADHD. Another possible factor in ADHD background is the dysregulation of the adrenergic system. The most frequently studied is the connection between polymorphism of norepinephrine transporter gene (NET), adrenergic receptors genes: alpha 2A (ADRA2A), alpha 1C (ADRA1C), alpha 2C and monoamine oxidase A gene (MAO-A).