Background The presence of anti-U1RNP is associated with the features of different systemic rheumatic diseases (SLE, SSc, etc.), and it is also included in the criteria of the mixed connective tissue disease (MCTD). It is important to note that the MCTD may evolve into other rheumatic diseases over time and only a third of patients have a stable clinical picture for many years. The frequency of detection of anti-U1RNP in SLE according to various studies varies from 13 to 40%. Our aim was to study the frequency of SLE among patients positive for anti-U1RNP.

Methods The study included 60 patients (pts) who were positive for anti-U1RNP: 54 women and 6 men, mean age 52±10 years, duration of the disease 10.6±8 years. All pts were examined according to guidelines.

Results In study group all pts were positive for ANAs, anti-U1RNP and met the criteria of MCTD (R. Kasukawa, 1987). The frequency of anti-DNA was 42%, anti-Ro – 38%, RF in 31%, anti-Sm 11%, anti-La – 8%. The detection of anti-DNA was correlated with the presence of overlap syndrome (r=0.3, p<0.05), the median indicator was 16.7 (5.2; 29.5), the range of values ranged from 0.1 to 300 IU/ml, while high values were detected in pts with a cross with SLE. Leukopenia was detected in 8 pts (14%), anemia – 2 pts (3%), hypocomplimentemia – 9 pts (15%), arthritis/arthralgia – 37 pts (62%), malar rash – 14 pts (24%). It turned out that 18 out of 60 (30%) pts with MCTD, it was possible to simultaneously establish the diagnosis of SLE (SLICC, 2012), thus the patients met the criteria for two different rheumatic diseases.

Conclusions 30% of patients positivity for anti-U1RNP simultaneously met the SLE criteria. This fact requires further study of this group of patients as a separate subtype of SLE.