To date, candidate genes, including SNAP‐25, dopamine receptor D4 protein (DRD4), dopamine receptor D5 protein (DRD5), dopamine transporter (DAT), dopamine beta‐hydroxylase (DBH), 5‐hydroxytryptamine transporter (5‐HTT) and 5‐hydroxytryptamine (serotonin) receptor 1B (5HT1B), have been identified from quantitative and molecular genetic studies, as well as ADHD animal models (Faraone et al., 2005; Gizer et al., 2009; Russell, 2011). Here, DRD5 is linked to attention deficit-hyperactivity disorder.