IGSF5 (immunoglobulin superfamily member 5) is a cell adhesion molecule that functions primarily in tight junction formation and cell-cell adhesion. The protein mediates calcium-independent homophilic cell adhesion and, together with MAGI1, provides an adhesion machinery at tight junctions that may regulate permeability in kidney glomerulus and small intestinal epithelial cells [UniProt annotation]. IGSF5 expression appears to have protective roles in multiple disease contexts. In colorectal cancer, genetic variants near IGSF5 are associated with advanced adenoma risk, with five variants in strong linkage disequilibrium located in or near the IGSF5 coding region showing significant association with advanced adenoma development 1. In head and neck squamous cell carcinoma, IGSF5 shows low expression, and overexpression significantly impairs cancer cell proliferation, suggesting a tumor suppressive function 2. The gene is also associated with asthma susceptibility, particularly in obese African American patients 3. Additionally, IGSF5 expression appears linked to cognitive health, as it may mediate associations between healthy dietary patterns and reduced dementia risk 4. Promoter polymorphisms in IGSF5 can significantly alter transcriptional activity, indicating functional genetic variation 5.