The impact of anti-U1-RNP positivity: systemic lupus erythematosus versus mixed connective tissue disease
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Anti-U1-RNP positivity remains mandatory for the mixed connective tissue disease (MCTD) diagnosis, reason for which anti-U1-RNP occurrence in patients with lupus clinical features might determine diagnostic issues. Thus, the prevalence of 25–30% for anti-RNP was reported in John Hopkins and LUMINA lupus cohorts and also 13% prevalence for the anti-U1-RNP in Euro-Lupus cohort. Presence of anti-U1-RNP antibodies in patients fulfilling SLE criteria (but not the MCTD ones) was associated with manifestations such as Raynaud phenomenon, musculoskeletal and lung impairment or nail fold capillaroscopy changes, some clinical features frequently encountered in MCTD patients and only rarely described in lupus population. The use of more specific markers such as 70 kDa anti-U1-RNP or anti-Sm-D was proposed for discriminating between SLE and MCTD. In addition, the IgM serotype of anti-U1-RNP seems more frequently expressed in SLE, while the IgG serotype alone in MCTD. Better acknowledgement of possible clinical involvements in lupus subsets, such as the peculiarities related to the anti-U1-RNP positivity, could provide access to early diagnosis of rather rare but possible severe lupus organ impairments (e.g. pulmonary arterial hypertension).
KeywordsU1 RNP U1 70 k Systemic lupus erythematosus Criteria MCTD Scleroderma
American College of Rheumatology
Connective tissue diseases
Diffuse connective tissue disease
Extractable nuclear antigen
Incomplete lupus erythematosus
Mixed connective tissue disease
Systemic lupus erythematosus
Systemic Lupus International Collaborative Clinics
Undifferentiated connective tissue disease
AD, CJ and CB conception and design. AD data acquisition. AD, CJ and CB analyzing and interpretation data. AD and CJ drafting the manuscript. CB revising the manuscript. AD, CJ and CB approval of the manuscript final version.
No specific grant from any public agency, commercial or not-for-profit sectors was received for the presented research.
Compliance with ethical standards
Conflict of interest
None of the authors received any fees, honoraria, grants or consultancies that would constitute a conflict of interest with the current study.
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