These data received support from genotypes for the trinucleotide repeat in the PPP3CA 5′UTR. The most frequent alleles for the 5′UTR trinucleotide repeat are distinguished by 8, 9, or 10 GGC repeats, forming the alleles that we denote as “B,” “C,” and “D,” respectively (Figure 3). In African–American samples, in which these three alleles display similar frequencies (B 0.35, C 0.20, D 0.42), there were significant, ca 10% “C” allele frequency differences between substance abuser and control samples (p = .03 after Bonferroni correction; Figure 3). D alleles were correspondingly more frequent in controls than in abusers, though the p-value was only 0.09 after Bonferroni correction. Corresponding odds ratios and confidence intervals were: OR = 1.75; CI = 1.16–2.63, for the C, and OR = 0.69; CI = 0.49–0.99, for the D alleles.
