DRD2 and substance abuse: At the DRD2 SNPs the association of the TaqIA polymorphism with substance abuse was marginally significant using the 3 genotype categories (χ2 = 5.34, df = 2, p = 0.069) and nominally significant for the A1+ vs A1- categories (χ2 = 4.52, df = 1, p = 0.034), with 57.9% of the substance abuse present group carrying the A1-allele vs 36.1% of the substance abuse absent group.