A number of association studies have focused on genes that are not as well studied as those mentioned in the previous section; these more exploratory studies are summarized in Table 2. These studies mostly focus on methamphetamine abuse-related phenotypes. These genes include CES1 (Nemoda et al. 2009); DTNBP1 (Kishimoto et al. 2008a); FZD3 (Kishimoto et al. 2008b); G72 (Kotaka et al. 2009); GABRG2 (Nishiyama et al. 2005); GLYT1 (Morita et al. 2008); GRM2 (Tsunoka et al. 2010); GSTM1 (Nakatome et al. 2009); GSTP1 (Hashimoto et al. 2004); GSTT1 (Nakatome et al. 2009); NQO2 (Ohgake et al. 2005); PDYN (Nomura et al. 2006); PICK1 (Matsuzawa et al. 2007); PROKR2 (Kishi et al. 2010); SLC22A3 (Aoyama et al. 2006); SNCA (Kobayashi et al. 2004) and SOD2 (Nakamura et al. 2006).
