with at least 1 copy of the ≥7 repeat allele and the DRD4-short (DRD4-S) group composed of individuals who had neither copy greater than 6 repeats. The observed frequency of the DRD4 and OPRM1 genotype combinations were: DRD4-S and OPRM1 Asn40, n = 43; DRD4-S and OPRM1 Asp40, n = 21; DRD4-L and OPRM1 Asp40, n = 29; and DRD4-L and OPRM1 Asp40, n = 12. The allele frequencies for the Asn40Asp SNP in this sample were in conformity with Hardy-Weinberg equilibrium expectations.
