No evidence for linkage between an insulin-dependent diabetes mellitus-susceptibility locus and immunoglobulin loci KM or GM.

We studied 52 families having more than one member affected with insulin-dependent diabetes mellitus (IDDM) for linkage of an IDDM-susceptibility locus to the immunoglobulin loci KM and GM. Linkage was analyzed by the LOD score method using single-locus recessive and dominant models of IDDM inheritance, with penetrances of the disease-susceptible genotypes being dependent on age and reaching a maximum of 20% by age 40. We found no evidence for linkage of IDDM to KM or GM. Close linkage (recombination fraction less than 5%) was rejected for KM under the recessive model and for GM under both models. These results suggest either that there are no IDDM-susceptibility loci closely linked to KM or GM or that use of a single-locus model of IDDM (which ignores the effects of the susceptibility locus in the HLA region) is inadequate for their detection.