COMT and major depressive disorder: Catechol-O-methyltransferase (COMT) (MIM 116790) catalyzes the transfer of a methyl group from S-adenosyl-methionine to catecholamines [1], and dopamine-beta-hydroxylase (DBH) (MIM 223360) catalyzes the conversion of dopamine to norepinephrine [2]; both enzymes are involved in the catecholamine metabolism system, in which abnormalities are hypothesized to be related to the development of psychiatric and neurological disorders such as schizophrenia and depression (for reviews, see [3,4]).