We scanned the genome in the European-American discovery cohort and identified a significant risk region between HTR1A and IPO11 on chromosome 5q at genome-wide significance level (Figures 1, 2 and 3), with the most significant SNP rs7445832 (p=6.2×10−9). We examined the 10Mb range surrounding this SNP, which covered the entire IPO11-HTR1A region (1.5Mb), in the discovery cohort, and found a total of 13 SNPs that had association signals for alcohol and nicotine co-dependence with p<10−4 (i.e., 6.2×10−9 ≤ p ≤ 9.1×10−5). These SNPs were concentrated within a narrow region (0.5Mb) surrounding the most significant SNP between IPO11 and HTR1A (Figure 2A).
