As part of an ongoing search for genes associated with type 1 diabetes (T1D), a common autoimmune disease, we tested the biological candidate gene IL2RA (CD25), which encodes a subunit (IL-2Ra) of the high-affinity interleukin-2 (IL-2) receptor complex. We employed a tag single-nucleotide polymorphism (tag SNP) approach in large T1D sample collections consisting of 7,457 cases and controls and 725 multiplex families. Tag SNPs were analyzed using a multilocus test to provide a regional test for

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... ssociation. We found strong statistical evidence in the casecontrol collection ( ) for a T1D locus in the CD25 region of chromosome 10p15 and replicated the 58 P p 6.5 # 10 association in the family collection ( ; combined ). These results illustrate the utility 53 510 P p 7.3 # 10 P p 1.3 # 10 of tag SNPs in a chromosome-regional test of disease association and justify future fine mapping of the causal variant in the region.