Fine‐mapping has identified two independent risk associations of T1D within the cluster of differentiation (CD)28‐cytotoxic T‐lymphocyte‐associated protein 4 (CTLA4) locus on chromosome 2: one near CD28, which is shared with CeD, and another intronic variant in CTLA4, shared with RA. Here, CD28 is linked to rheumatoid arthritis.