Anti-U5 snRNP antibody as a possible serological marker for scleroderma-polymyositis overlap

Abstract

Objective. To determine the prevalence of the anti-U5 small nuclear ribonucleoprotein (snRNP) antibody in patients with systemic sclerosis. Methods. Sera from 281 patients with systemic sclerosis, including 10 patients with overlapping polymyositis, were assayed using RNA immunoprecipitation and protein immunoprecipitation. Results. Only one serum sample showed precipitation of U5 snRNA with scarce precipitation of U2, U1, U4 and U6 snRNAs. In addition, the serum precipitated a 200 kDa protein. The serum was from a 35-yr-old Japanese male patient with overlapping systemic sclerosis and polymyositis accompanied by large-cell lung carcinoma. The clinical appearance was similar to that of a case reported previously. Conclusion. The presence of the anti-U5 snRNP antibody in serum may be specific for scleroderma-polymyositis overlap syndrome.