After mapping significantly associated SNPs from the GWAS meta-analysis to likely causal genes, we explored which tissues or cell types showed enriched gene expression of OCD-associated genetic signals using a previously described approach29 on published human gene expression datasets from bulk tissue RNA-seq data from the Genotype–Tissue Expression (GTEx) project and single-cell RNA-sequencing data from the adult mouse central and peripheral nervous systems30. We found enrichment of OCD GWAS signals in six of 13 human brain tissue types in GTEx but no enrichment in human peripheral tissues (Fig. 2b and Supplementary Table 15). In the adult mouse central and peripheral nervous systems, we found enrichment of OCD GWAS signals in 41 of 166 tested specific single cell types using the MAGMA gene set enrichment test (Supplementary Table 16). When summarizing results of individual single cell types into groups of cell types defined by the same region or tissue and cell type, nine of 35 were enriched for OCD GWAS signals (top 20 shown in Fig. 2c). Strong enrichment of OCD GWAS signal was especially observed in excitatory neurons of the hippocampus and the cerebral cortex as well as in D1 and D2 medium spiny neurons (MSNs).
