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

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.