Association studies are a potentially powerful approach to identifying susceptibility variants for common multifactorial diseases such as type 1 diabetes, but the results are not always consistently reproducible. The IDDM5 locus has recently been narrowed to an approximately 200-kb interval on chromosome 6q25 by two independent groups. These studies demonstrated that alleles at markers in the mitogen-activating protein kinase 7 interacting protein 2 (MAP3K7IP2)/SUMO4 region were associated with susceptibility to type 1 diabetes. Subsequent studies, however, showed inconsistency in the association of the SUMO4 gene with type 1 diabetes. To clarify the contribution of the M55V polymorphism of the SUMO4 gene to type 1 diabetes susceptibility, 541 type 1 diabetic patients and 768 control subjects were studied in Asian populations. The M55V polymorphism was significantly associated with type 1 diabetes in Asian populations (summary odds ratio [OR] 1.46, P = 0.00083, Mantel-Haenszel test). Meta-analysis of published studies and the present data confirmed a highly significant association in Asian populations (summary OR 1.29, P = 7.0 x 10(-6)) but indicated heterogeneity in the genetic effect of the SUMO4/MAP3K7IP2 locus on type 1 diabetes among diverse ethnic groups. These data indicate that the MAP3K7IP2/SUMO4 locus in the IDDM5 interval is associated with type 1 diabetes in Asian populations.