The intron 2 SNP, rs11503014, is not located within a haplotype block (Figure 1). The homozygote 11 frequency (0.33) and the heterozygote 12 frequency (0.36) in heroin addicted men were very similar and together differed significantly from the homozygote 22 frequency (0.23) (p = 0.003). The mean total CTQ score for the homozygote 11 and heterozygote 12 individuals were very similar (46.1, SD = 15.2 and 46.9, SD = 18.5 respectively) and together differed from that of the homozygous 22 individuals (43.6, SD = 15.5), p = 0.039. Thus these results provided the justification for combining the 11 and 12 genotypes in order to increase statistical power in the smaller data subsets.
