We found 311 splicing TWAS associations with disordered alcohol use (padj < 0.05; 215 unique genes; see Supplementary File S7), which were enriched for alcohol dehydrogenase activity (padj = 3.23e−10). Seven of the TWAS splicing genes were also differentially spliced genes in post-mortem brain tissue (GRK4, KLHDC8B, PDS5A, PSMD7, TMEM184B, VRK2, and WDR27). The role of these genes in the pathophysiology of AUD is largely unknown. Previous research suggests that SNPs mapped to these genes are associated with substance use traits, neuropsychiatric illnesses, and neurological endophenotypes as well as other unrelated traits (see Supplementary File S8). Of note, our lead sQTLs for the GRK4 (rs2858038) and KLHDC8B (rs3819325) genes were in LD with SNPs associated with human cigarettes per day (rs2960306, R2 = 0.29) and smoking cessation (rs7617480, R2 = 0.07)35. To investigate potential shared genetic processes across substance use, we correlated significant splicing TWAS associations across three substance use traits: cigarettes per day35, opioid use disorder36, and cannabis use disorder37. Using the 1397 significant splicing TWAS associations across substance use traits (BH-FDR < 0.05; 923 unique genes; see Supplementary File S9), we found substantial overlap—especially among disordered substance use (all r > 0.38; see Supplementary Fig. S8).
