Characteristics of patients with serum antibodies to extractable nuclear antigens.

A distinguishing feature of the mixed connective tissue disease (MCTD) syndrome is the presence in the serum of antibody in high titer to ribonucleoprotein (RNP). To determine whether this was an exclusive observation, a large rheumatic disease population was surveyed for the presence of antibody in high titer to extractable nuclear antigens (ENA) including RNP. Of 650 sera examined, 440 (from 240 patients) had antinuclear antibody. Only 39 patients had serum antibody to ENA in titers greater than or equal to 1:200 dilution. In 16 the anti-ENA was shown by RNAse digestion to be anti-RNP. Although many clinical and laboratory characteristics were similar in these two groups, the patients more closely resembled the previously described MCTD syndrome and, importantly, less often had severe renal and central nervous system disease manifestations. Thus the presence of serum antibodies to ENA that are predominantly RNAse-sensitive (anti-RNP) helps to identify a rheumatic disease syndrome and also appears to have prognostic value.