COMT is a degradatory enzyme for catecholamines. The most well-researched polymorphism in COMT (22q11.21) is the common G>A transition (rs4680), which results in a valine to methionine substitution (Val158Met) and a decrease in enzyme activity by 3- to 4-folds (Lachman et al., 1996). Many studies have investigated the association between the low-activity allele (Met) and AD with inconsistent results (Köhnke, 2008). Investigators have reported associations between this SNP and methamphetamine abuse (Bousman et al., 2009) and NS (Golimbet et al., 2007; Tsai et al., 2004), while Cheuk and Wong’s (2006) meta-analysis estimated no association with ADHD.
