Four top SNPs associated with CPD span approximately 100 kb (76.6–76.7 Mb) at 15q25.1; from rs3813570, located in the 5′-untranslated region (c.-72T>C) of PSMA4, to rs938682, located in IVS4 (c.378-1941C>T) of CHRNA3 (Table 2 and Figure 2). The most significant SNP, rs2036527, is located between PSMA4 and CHRNA5, and is correlated with the index signals (rs1051730, rs16969968) for CPD reported in previous European ancestry studies. In CEU, the r2 is 0.84 between rs2036527 and rs1051730, and 0.93 between rs2036527 and rs16969968. The r2 between rs2036527 and 1051730 is 0.44 in YRI, and 0.502 in STOMP, whereas rs16969968 is non-polymorphic. Rs2036527 is also correlated with SNPs in the European Americans that tag a haplotype associated with increased expression of CHRNA5 in prefrontal cortex brain samples from European Americans and African Americans,40 but is not correlated with this haplotype in African ancestry samples (r2 between rs2036527 and rs1979905=0.443 in CEU, 0.045 in YRI and 0.064 in STOMP). The additional signals at 15q25.1 with near genome-wide significance in our study are represented by rs667282, rs938682 and rs3813570, which are weakly correlated with rs2036527
