Overview of the workflow used in this study. 1) Meta-GWAS of 256 diseases and disease traits (left) revealed Th differentiation (right) to be the pathway most enriched for GWAS genes. 2) Identification of disease modules in eight CD4+ T-cell-associated diseases (A, allergy; AML, acute myelogenous leukemia; ATL, adult T cell leukemia; CLL, chronic lymphocytic leukemia; HES, hypereosinophilic syndrome; MS, multiple sclerosis; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus). These modules partially overlapped and formed a pleiotropic module. The pleiotropic module is marked using a solid black circle. 3) The pleiotropic module was highly enriched for genes relevant to many diseases. 4) Prospective clinical studies of multiple sclerosis and seasonal allergic rhinitis showed that pleiotropic and disease-specific genes could stratify patients for individualized medication.