Allele and genotype frequencies of DRD2 polymorphism are shown in Tables 2 and 3, respectively. Genotype frequencies were in Hardy-Weinberg equilibrium in the control group (χ2 = 2.01, df = 1, P = 0.16) but not in the patient group (χ2 = 5.20, df = 1, P = 0.022), probably because, as described below, the latter group was enriched in A1-A1 homozygotes. A1 allele frequencies were not statistically significantly different between patients and controls (χ2 = 2.18, df = 1, P = 0.140). Both groups differed in genotype frequency (χ2 = 6.48, df = 2, P = 0.039). Notably, the A1-A1 genotype was detected in 7.1% of patients and 1.4% of controls (χ2 = 6.43, df = 1, P = 0.011, odds ratio = 5.48 [95% CI 1.26–23.78]).
