[The value of RNase-ANA determinations for the diagnosis of Sharp syndrome (mixed connective tissue disease) (author's transl)].

The presence of antinuclear antibodies with speckled pattern is essential for the diagnosis of the Sharp Syndrome (moxed connective tissue disease=MCTD). It is however not a specific finding seen only in this condition. Antinuclear antibodies (ANA) with speckled pattern can be observed in sera of patients with various rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus, Sjögren Syndrome) and even in healthy persons. Yet, utilizing the differentiation system of the antinuclear antibodies, it seems to be possible to establish the diagnosis of mixed connective tissue disease. The antinuclear antibodies in mixed connective tissue disease show high titres (1:2560--1:20,480), contain IgG and bind complement. The antigen is a ribonucleoprotein (RNP) which is sensitive to ribonuclease treatment. The latter observation allows a differentiation between the ANA in mixed connective tissue disease and the ANA in other conditions, especially in systemic lupus erythematosus and Sjögren Syndrome.