Linkage of rheumatoid arthritis to insulin-dependent diabetes mellitus loci - Evidence supporting a hypothesis for the existence of common autoimmunesusceptibility loci

Objective. To seek potential autoimmune disease susceptibility loci by test ing for linkage and linkage disequilibrium between insulin-dependent diabet es mellitus (IDDM) susceptibility loci and rheumatoid arthritis (RA), Methods, Five IDDM susceptibility loci map to 2 chromosomal regions, chromo some 2q31-34 (IDDM7, 12, and 13) and chromosome 6q25-27 (IDDM5 and 8), Micr osatellite markers within these regions were genotyped in 255 RA families, by fluorescence-based genotyping technology. Evidence for linkage disequili brium was assessed using the extended transmission disequilibrium test (ETD T) program. Results, With the ETDT, we found evidence for linkage disequilibrium of the marker D6S446, at IDDM8, with RA (P < 0.0001), There was additional eviden ce for linkage disequilibrium with 2 markers at IDDMS (D6S311 and D6S440) ( P = 0.016 and P = 0.017, respectively). There was no evidence for significa nt linkage disequilibrium of RA with any markers at IDDM7, 12, or 13. Conclusion. These results support the hypothesis that there are autoimmune disease genes at IDDMS and IDDM8.