The possible association between A118G polymorphism and different substance use disorders has been investigated in several studies (reviewed by van der Zwaluw et al., 2007 and Mague and Blendy, 2010). The results have been inconsistent. With respect to alcohol dependence, several case–control studies have reported significant associations or trends between alcohol dependence and the G allele (Rommelspacher et al., 2001; Bart et al., 2005; Nishizawa et al., 2006; Kim et al., 2009), whereas some groups have not found any association (Bergen et al., 1997; Sander et al., 1998; Gelernter et al., 1999; Kim et al., 2004a; Loh el et al., 2004; Zhang et al., 2006). Yet a few studies, including a recent study with a large study population, have reported the A allele as a risk allele (Town et al., 1999; Schinka et al., 2002; Du and Wan, 2009, Koller et al., 2012). In a meta-analysis including 10 studies with alcohol dependence as a main diagnosis, no significant association was found between the polymorphism and alcohol dependence (Arias et al., 2006), whereas a more recent meta-analysis including 12 studies, 5
