Furthermore, we did not detect any signal with COMT’s well-studied functional polymorphism rs4680, which has been associated with a number of disinhibitory phenotypes, including AD (Köhnke, 2008), methamphetamine abuse (Bousman et al., 2009), and NS (Golimbet et al., 2007; Tsai et al., 2004). One explanation for this may be that none of the potential risk alleles were found in our population. It is noteworthy that the SNP in DDC (rs11575542, p = 0.0028, β = 0.80) that we identified as associated with DD symptoms is a missense coding polymorphism that results in a substitution from Arg to Gln; however, the MAF of this SNP in our sample is only 1.5%, which increases the likelihood that it is a false positive.
