In single marker analyses, 14 SNPs defining two independent genomic intervals achieve genome-wide significance, 13 within the collagen VI A3 (COL6A3) gene on chromosome 2q37.2 (Figure 3A), including the most significant SNP in our study, rs2256485, p=6.17×10−9 (Table 1). COL6A3 encodes an extracellular matrix (ECM) protein expressed in brain. Although there is no prior human association evidence for this gene, remodeling of the ECM has been strongly implicated in response to various drugs of abuse (Lubbers et al., 2014). The second interval is defined by a single SNP (rs150268941, p=1.65×10−8, Table 1) on chromosome 3q26.31 (Supplementary Figure S5A).
