Two hundred and four male patients (103 Russians and 101 Tatars), aged 13-45 years old, were studied. All were diagnosed as opiate drug addicts and hospitalized at the Republican Center of Narcology in Ufa, Russia. Two hundred and eight practically health males (105 Russians and 103 Tatars) in the same age group formed a control sample.

      DNA was extracted by a phenol-chloroform method [16]. The following primers for TaqI A (located in the 3'UTR) and NcoI (located on exon 6) restriction polymor­phisms of D2 dopamine receptor gene (DRD2) were used: locus TaqI A [2] 5’-CCG TCG ACG GCT GGC CAA GTT GTC TA-3’; 5’-CCG TCG ACC CTT CCT GAG TGT CAT CA-3’; locus NcoI [3] 5’-ATC CTG CAG CCA TGG-3’; 5’-ATT GTC CGG CTT TAC C-3’. After initial denaturation (at 94EC for 3 min.), 35 cycles of annealing of primers for 1 min. at 58EC; DNA synthesis for 1 min. at 72EC; denaturation for 1 min. at 94EC, were performed; final extension was at 72EC for 10 min. [5]. To 10 mL of reaction mixture, 5 units of restriction endo­nuclease, TaqI A or NcoI, were added. Alleles A1 of TaqI A (310 bp) and N1 of NcoI (480 bp) were left intact, while alleles A2 and N2 underwent spontaneous hydrolysis. The A2 allele fragments were 130 and 180 bp long, and the N2 allele fragments, 194 and 252 bp long.

      The following primers for the VNTR polymorphism of DATI gene were used [9]: 5’- TGT GGT GTA GGG AAC GGC CTG AG-3’; 5’-CTT CCT GGA GGT CAC GGC TCA AGG-3’. After initial denaturation (at 95EC for 4 min.) 32 cycles were performed. Annealing of primers for 30 seconds at 68EC; DNA synthesis for 1.5 min. at 72EC; denaturation for 30 seconds at 95EC; final extension for 10 min. at 72EC [14]. Amplified fragments of DNA were separated by electrophoresis on native 6% polyacrylamide gel, stained with ethidium bromide and visualized under UV light.

      For statistical analysis we used a modified a chi-square test using an RxC (Rows x Columns) computer program, based on the published algorithm [17]. Relative risk (OR: odds ratio) was calculated following the formula in [18] with OR = 1 taken as no association, OR >1 as positive association of disease with allele or genotype (risk factor), and OR <1 as negative association (resistance factor).