Among polygenes conferring susceptibility to type I diabetes in the NOD mouse, Iddlo oil distal chromosome 3 has been shown to be important for disease susceptibility. In this Study, we investigated the candidacy of Fcgr1 and Cd101 for Idd10, by congenic mapping and candidate gene sequencing. Among seven NOD-related strains Studied. the IIS Mouse Was found to possess a recombinant Idd10 interval with the same sequence at Fegr1 as the NOD mouse, but a different sequence at Cdl10 from that in the NOD mouse with 10 amino acid Substitutions. The frequency of type 1 diabetes in NOD mice congenic for IIS hid10 (NOD.IISIdd10) was significantly reduced as compared to that in the NOD Mouse. despite the presence of the identical Fegr1 sequence. These data indicate that IIS mice possess a resistant allele at Idd10, and Suggest that Cd101. but not Fegr1. is responsi tile for the Idd10 effect. © 2005 Elsevier Inc. All rights reserved.