To seek additional information from these PPP3CA variants in substance abuse vulnerability, we genotyped additional simple sequence repeat and SNP markers in abuser/control populations of European and/or African-American descent (Tables 1 and 2, respectively). In African–American samples, there was a nominally significant genotype frequency difference for the 5′ 16 nucleotide repeat intron 1 VNTR, ss68756205 (p = .024) [Figure 1(A) and Table 2].
