In the context of HAND, the dopamine-related genes that have been studied include genes for: catechol-O-methyltransferase (COMT), an enzyme involved in dopamine metabolism; the dopamine transporter (DAT), the channel for the re-uptake of dopamine from the synaptic cleft; brain-derived neurotrophic factor (BDNF) which is involved in regulating dopaminergic and serotonergic activity; and dopamine beta-hydroxylase. Here, BDNF is linked to HIV-associated neurocognitive disorder.