The gene-based association results are displayed in the last two rows of Table 2. Specifically, we included 39 SNPs in NCK2. The P values from the gene-NCK2-based tests that were obtained through the standard allelic test and logistic regression are 3.12 × 10−10 and 2.70 × 10−6, respectively. The gene-based P value from the standard allelic test reached the genome-wide significance at gene level. The gene-based P value through logistic regression is very close to the gene-based genome-wide significance level. Therefore, both methods provided significant evidence that supports the association between the NCK2 gene and opiates dependence in African-origin men. For the addiction of the other five substances in African-origin men, nicotine dependence had the most significant association with the NCK2 gene (P = 9.56 × 10−3).
