Mixed connective tissue disease. Appearance of antibodies to ribonucleoprotein following corticosteroid treatment.

Antibodies to ribonucleoprotein are the serological marker of mixed connective tissue disease (MCTD). Five patients are presented who had negative or low titer anti-RNP antibodies despite characteristic MCTD. In all 5 patients antibodies to RNP appeared after they had taken prednisone for periods ranging from 3 wk to 15 months.