We used GUESSFM to fine map the association of multiple sclerosis (MS) and type 1 diabetes (T1D) to an established susceptibility region for immune-mediated diseases on chromosome 10p15 (S1 Fig), which contains the candidate causal gene IL2RA. IL2RA encodes a subunit CD25 (IL-2RA) of the interleukin 2 (IL-2) receptor that is essential for the high affinity binding of IL-2 [14]. The gene discussed is IL2; the disease is type 1 diabetes mellitus.