We found substantial differences between the EA and AA samples in the allele frequencies for several SNPs (Table 2). The presence of these allele frequency discrepancies suggests genetic differences underlying ND. To eliminate any potential effect of ethnic differences on our association results, we performed independent association analyses within the individual samples. For the AA sample, rs8040868 within CHRNA3 was significantly associated with all three adjusted ND measures (P = 0.017 to 0.039); however, no association remained significant after correction for multiple testing. No significant association with ND was detected for any individual SNP in the three genes.
