Several common population SNPs of COMT were significant in genome-wide association studies of addictive behavior, cognition, and mood and neurological disorders (Egan et al, 2001; Shifman et al, 2002; Bray et al, 2003; Meyer-Lindenberg et al, 2006; Hendershot et al, 2012; Guillot et al, 2015; Lin et al, 2017). Here, COMT is linked to nervous system disorder.