Objective: To study the serologic status of 3 previously unreported monozygotic twin pairs discordant for systemic sclerosis (SSc).
Methods: Autoantibodies were measured by indirect immunofluorescence, immunodiffusion, and immunoprecipitation of 35S-labeled cell lines. Major histocompatibility complex (MHC) class II allele typing and DNA fingerprinting were used to confirm monozygosity.
Results: Anti-PM-Scl, anti-threonyl transfer RNA synthetase, and anti-topoisomerase I antibodies, respectively, were found in each of the twins with SSc. None of the unaffected twin siblings had an identifiable autoantibody, although serum from 1 unaffected twin precipitated several unknown proteins. The MHC class II genotype in each twin was the genotype expected for the autoantibody that was present.
Conclusion: Autoantibodies of certain defined specificities are intimately linked with the development of SSc, because they segregate with SSc in individuals who start life with identical germline genes.