Catechol-O-methyltransferase (COMT) is an enzyme that catalyses the transfer of a methyl group from S-adenosylmethionine to any catechol-containing molecule, this is an important step in the degradation of families of molecules such as the catecholamines (dopamine, epinephrine and norepinephrine Guldberg & Marsden, 1975; Weinshilboum, Otterness, & Szumlanski, 1999) and the catecholoestrogens (Ball, Knuppen, Haupt, & Breuer, 1972). The COMT gene includes a number of single nucleotide polymorphisms (SNPs), the most commonly studied being