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Various clinical and immunological phenotypes of systemic sclerosis (SS) differ in the frequency and severity of manifestations of the disease, the progression of damage to internal organs, and prognosis. The detection rate of anti-U1-ribonucleoprotein (RNP) (anti-U1RNP) antibodies in SSD ranges from 5 to 30%. They are found in various rheumatic diseases (SS, systemic lupus erythematosus, rheumatoid arthritis, polymyositis, and Sjo gren’s syndrome) and are associated with a more favorable course, a good response to treatment (in particular, that with glucocorticoids), and a good prognosis. In SS, the clinical and laboratory associations of anti-U1RNP have been insufficiently investigated. Objective: to compare clinical, laboratory, and instrumental findings in patients with SS positive for anti-U1RNP, anti-topoisomerase-I (anti-Scl70), and anticentromere antibodies (ACA). Subjects and methods. Sixty-five anti-U1RNP antibody-positive patients were selected for a study group (Group 1) from the general database of patients who met the 2013 ACR/EULAR criteria for SS and who were followed up at the V.A. Nasonova Research Institute of Rheumatology in 2012 to 2017. The comparison groups included 50 anti-Scl70 antibody-positive patients with SS (Group 2) and 50 ACA-positive ones (Group 3). Anti-U1RNP negativity was confirmed in patients of the comparison groups. Results and discussion . Most patients in Groups 1 and 3 had the limited type of SS (88 and 94%, respectively) and a chronic course of the disease (82 and 94%) while Group 2 patients showed an acute and subacute course (52%) and predominantly the diffuse type of SS (58%). All the patients with SS had a higher level of antinuclear factor. The feature of the anti-U1RNP positive group was a preponderance of the limited type of the disease with minimal skin damage concurrent with a more frequent involvement of the musculoskeletal system (damages to the joints (65%) and muscles (43%), as well as with the high rate of damage to internal organs (in particular, the lung, heart, and gastrointestinal tract). The patients of this group exhibited high inflammatory and immunological activities, hematological disorders (hypocomplementemia (15%) and leukopenia (14%)). Sjo gren’s syndrome was detected in one-third of these patients. Conclusion. Further study of anti-U1RNP-positive SS will be able to create a management algorithm and to more clearly define the risks and prognosis of the disease for this group of patients.

Among the patients fulfilling the criteria for systemic sclerosis (SS), there is a subgroup without SS-specific antinuclear antibodies, but positive for anti-ribonucleoprotein (anti-U1 RNP) antibodies. The clinical significance of this type of antinuclear antibodies in SS is not clear. The presence of anti-U1 RNP antibodies is of great interest, since they are not only present in other rheumatic diseases, but are also considered as a marker for mixed connective tissue disease. Objective : to reveal the frequency of anti-U1RNP antibodies in patients with SS and to provide the clinical and laboratory characteristics of patients positive for these antibodies. Subjects and methods . 330 patients who fulfilled the 2013 ACR/EULAR criteria for SS and had been followed at the V.A. Nasonova Research Institute of Rheumatology from 2012 to 2017 were included. Anti-U1 RNP were determined by enzyme immunoassay (reference values: 0–25 U/ml). Results and discussion . Anti-U1RNP were detected in 65 (19.7%) patients with SS (85% of patients were highly positive; 15% were low-positive). The group included 8 men and 57 women; their mean age was 46±14 years. The disease duration was 11±7.9 years. Skin lesions were minimal; 59 (91%) patients had a limited form of the disease with swelling in the hands (scleredema) in 40% of cases and sclerodactyly in 60%. Raynaud's phenomenon was present in all the patients. One-half of the cases were observed to have peripheral ischemic disorders: digital scars and/or sores (43%), as well as necroses and ulcers of other sites, which were relatively rare (8%). Interstitial lung disease (ILD) was identified in 63% of cases. Elevated pulmonary artery systolic pressure (PASP) ≥40 mm Hg, as shown by echocardiography, was detected in 26% of cases and was associated mainly with the presence of ILD; pulmonary arterial hypertension was confirmed in three patients. Esophageal lesions were found in 61% of patients. One-third of patients had signs of scleroderma cardiopathy. The feature of the group was the common involvement of the locomotor system: joints with arthralgia and/or synovitis in 65% and muscles with mild and moderate myopathy in 43%. Erythrocyte sedimentation rate (ESR) and C-reactive protein levels were frequently elevated. The concurrence with Sjo gren's syndrome was common (in one-third of patients). None case of scleroderma renal disease was recorded; the mean values of kidney function were within the normal range; however, the glomerular filtration rate was lower than 80 ml/min/m2 in 17% of patients. All the patients were positive for antinuclear factor (HEp-2); in addition, there was rheumatoid factor (22%), antibodies against Ro/SS-A (41%), La/SS-B (18%), double-stranded DNA (42%), Scl70 (7%), and anticentromere antibodies (9%); 39 out of the 55 (71%) patients who were highly anti-U1 RNP-positive fulfilled the mixed connective tissue disease criteria proposed by R. Kasukawa et al. (1987). Conclusion . The investigation allows one to discuss of the presence of a special phenotype of SS, which is characterized by peculiar clinical manifestations in the presence of anti-U1 RNP overproduction.