Type 1 Diabetes in the

OBJECTIVE—Two type 1 diabetes susceptibility genes have been identified in the spontaneously diabetic biobreeding diabe-tes-prone (BBDP) rat, the major histocompatibility complex (MHC) (RT1) class II u haplotype (Iddm1) and Gimap5 (Iddm2). The strong effects of these have impeded previous efforts to map additional loci. We tested the hypothesis that type 1 diabetes is a polygenic disease in the BBDP rat. RESEARCH DESIGN AND METHODS—We performed the most comprehensive genome-wide linkage analysis for type 1 diabetes, age of disease onset (AOO), and insulitis subpheno-types in 574 F2 animals from a cross-intercross between BBDP and type 1 diabetes–resistant, double congenic ACI.BBDP-RT1u,Gimap5 (ACI.BB1u.lyp) rats, where both Iddm1 and Iddm2 were fixed as BBDP. RESULTS—A total of 19 % of these F2 animals developed type