Furthermore, we identified variants in GRM8 (Glutamate Metabotropic Receptor 8; rs2157752, p=5.32E-09, chr.7), important for mediating reward-related learning and memory, and in BDNF (rs6265, p=7.98E-10, chr. 11), a candidate gene in genetic studies of substance use disorders given its role in synaptogenesis and memory. None of the lead SNPs showed evidence of heterogeneity across cohorts, based on the I2 index (Supplementary Figure 4). Combining these data with UKBB (which uses a less stringent TUD definition, TUD-multi+UKBB) yielded fewer lead SNPs (Supplementary Table 8).
