Studies have also examined the moderating effect of the Asn40Asp SNP in OPRM1 on naltrexone treatment response in alcohol-dependent individuals and in samples of non-treatment-seeking heavy drinkers. Oslin et al. (2003), in a study of 130 EA subjects from three placebo-controlled trials, found that naltrexone-treated patients with one or more Asp40 alleles were significantly less likely than Asn40 homozygotes to relapse to heavy drinking. Placebo-treated subjects showed no moderating effect of genotype. Gelernter et al. (2007) examined the moderating effect of polymorphic variation in opioid receptor genes on treatment response in a subset of patients from the VA Cooperative Study of Naltrexone Treatment (Krystal et al. 2001). In addition to the Asn40Asp polymorphism, these investigators studied two other OPRM1 SNPs, three markers in OPRD1 (which encodes the delta-opioid receptor), and one marker in OPRK1 (which encodes the kappa-opioid receptor). They found no significant interaction between any of the SNPs studied and the response to naltrexone treatment. Anton et al. (2008) examined the moderating effect of the Asn40Asp SNP on the response to naltrexone treatment in a sub-sample of 297 EA
