Anti-U1RNP antibodies are associated with a distinct clinical phenotype and a worse survival in patients with systemic sclerosis.

Objectives: To clarify the impact of anti-U1RNP antibodies on the clinical features and prognosis of patients with SSc.
Methods: We conducted a monocentric case-control, retrospective, longitudinal study. For each patient with SSc and anti-U1RNP antibodies (SSc-RNP ⁺ ), one patient with mixed connective tissue disease (MCTD) and 2 SSc patients without anti-U1RNP antibodies (SSc-RNP ^- ) were matched for age, sex, and date of inclusion.
Results: Sixty-four SSc-RNP ⁺ patients were compared to 128 SSc-RNP ^- and 64 MCTD patients. Compared to SSc-RNP ^- , SSc-RNP ⁺ patients were more often of Afro-Caribbean origin (31.3% vs. 11%, p < 0.01), and more often had an overlap syndrome than SSc-RNP ^- patients (53.1 % vs. 22.7%, p < 0.0001), overlapping with Sjögren's syndrome (n = 23, 35.9%) and/or systemic lupus erythematosus (n = 19, 29.7%). SSc-RNP ⁺ patients were distinctly different from MCTD patients but less often had joint involvement (p < 0.01). SSc-RNP ⁺ patients more frequently developed interstitial lung disease (ILD) (73.4% vs. 55.5% vs. 31.3%, p < 0.05), pulmonary fibrosis (PF) (60.9% vs. 37.5% vs. 10.9%, p < 0.0001), SSc associated myopathy (29.7% vs. 6.3% vs. 7.8%, p < 0.0001), and kidney involvement (10.9% vs. 2.3% vs. 1.6%, p < 0.05). Over a 200-month follow-up period, SSc-RNP ⁺ patients had worse overall survival (p < 0.05), worse survival without PF occurrence (p < 0.01), ILD or PF progression (p < 0.01 and p < 0.0001).
Conclusions: In SSc patients, anti-U1RNP antibodies are associated with a higher incidence of overlap syndrome, a distinct clinical phenotype, and poorer survival compared to SSc-RNP ^- and MCTD patients. Our study suggests that SSc-RNP ⁺ patients should be separated from MCTD patients and may constitute an enriched population for progressive lung disease.
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