Immune-Related Mendelian Randomization Signals for Anxiety Disorders Highlight the CD40 Locus on Chromosome 20 (chr20:46118–46130 Mb, GRCh38)

Background/Objectives: Although genetic studies have linked immune phenotypes with anxiety, broad Mendelian randomization (MR) screens require explicit multiple-testing control. We reappraised 1753 reported immune-cell-trait-to-anxiety inverse-variance-weighted (IVW) association records available in the analysis tables and assessed the chromosome 20 signal that includes CD40. Methods: The reported records were derived from the 731-trait Sardinian flow-cytometry GWAS of Orrù et al. and were evaluated across one UK Biobank and three FinnGen anxiety phenotypes; outcome-specific Benjamini–Hochberg false-discovery-rate (FDR) correction was applied to the available analysis table. The leading locus was examined using bulk and single-cell expression quantitative trait locus annotations, two-sample MR, summary-data-based MR (SMR), HEIDI tests, and regional colocalization results. Results: Of 1753 tests, 120 were nominally significant, and 21 were retained after outcome-specific FDR correction (14 for UK Biobank anxiety and 7 for FinnGen all anxiety; none for generalized or phobic anxiety). B-cell and regulatory/CD4 T-cell traits were common among retained associations, and several B-cell traits mapped to variants at the CD40 locus. For FinnGen all anxiety disorders, monocyte instruments gave a positive estimate (beta = 0.00418, p = 9.25 × 10−4), whereas three naïve B-cell instruments gave a negative estimate (beta = −0.0520, p = 2.64 × 10−4). Monocyte SMR was null (p = 0.542). Naïve B-cell SMR was nominally significant (p = 0.00537), but HEIDI could not be calculated. Regional colocalization was weak in both cell contexts (PP.H4 = 0.0205 and 0.00272). Conclusions: The post-selection locus follow-up prioritizes a chromosome 20 immune locus but does not establish CD40-mediated regulation of anxiety. Because the upstream screen was not regenerated from source GWAS files and complete per-instrument F-statistics were unavailable, all findings are exploratory. CD40 remains a testable candidate for ancestry-matched fine-mapping and cell-state-specific validation.