To match the significant SNPs to the genes whose function they likely influence, we conducted a series of positional and functional gene mapping analyses. The positional mapping employed MBAT-combo19, while the functional mapping tested whether genetic variants associated with OCD were also associated with differential expression of nearby genes (within 1-Mb window) using (i) transcriptome-wide association study (TWAS)20 utilizing PsychENCODE data and included colocalization with COLOC27,28 and (ii) summary-based Mendelian randomization (SMR22) using whole-blood eQTL information and brain tissues from MetaBrain, alongside the HEIDI test which tests for heterogeneity in GWAS signal and eQTL association. Further, a protein-wide association study (PWAS) was conducted. As a final step, genes within each locus were prioritized using PsyOPS26, which integrates both positional and functional information. The details of each method are described below.
