“…In particular, two polymorphisms in exon 1 of the gene alter amino acid sequence, A +118 G (Asn40Asp) and C +17 T (Ala6Val), and these have received the most research attention. However, case-control studies have failed to demonstrate a consistent association between OPRM1 sequence variation and the presence of alcohol and/or drug dependence (Bergen et al, 1997;Berrettini et al, 1997;Bond et al, 1998;Kranzler et al, 1998;Sander et al, 1998;Gelernter et al, 1999;Town et al, 1999;Hoehe et al, 2000;Franke et al, 2001;Rommelspacher et al, 2001;Szeto et al, 2001;Schinka et al, 2002;Crowley et al, 2003).…”