26rhk236 10.3205/26rhk236 urn:nbn:de:0183-26rhk2366 Meeting Abstract de Vries de Vries Dewi Marina DM

Medizinische Fakultät, Universität zu Köln, Klinik II für Innere Medizin, Rheumatologie, Köln, Deutschland

author Steiner Steiner Joachim J

Medizinische Fakultät, Universität zu Köln, Klinik II für Innere Medizin, Rheumatologie, Köln, Deutschland

author Kubacki Kubacki Torsten T

Medizinische Fakultät, Universität zu Köln, Klinik II für Innere Medizin, Rheumatologie, Köln, Deutschland

author German Medical Science GMS Publishing House

Düsseldorf

610 20260909 engl This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. Dieser Artikel ist ein Open-Access-Artikel und steht unter den Lizenzbedingungen der Creative Commons Attribution 4.0 License (Namensnennung). M0656 236 Deutsche Gesellschaft für Rheumatologie Deutsche Gesellschaft für Orthopädische Rheumatologie Gesellschaft für Kinder- und Jugendrheumatologie 54. Kongress der Deutschen Gesellschaft für Rheumatologie und Klinische Immunologie (DGRh), 36. Jahrestagung der Gesellschaft für Kinder- und Jugendrheumatologie (GKJR), 40. Jahrestagung der Deutschen Gesellschaft für Orthopädische Rheumatologie (DGORh) Deutscher Rheumatologiekongress 2026 Vaskulitiden & Kollagenosen Leipzig 20260909 20260912 VK.10 TextIntroduction: Anti-U1 ribonucleoprotein (U1RNP) antibodies are characteristic of mixed connective tissue disease (MCTD) but are also detected in other connective tissue diseases, particularly systemic lupus erythematosus (SLE). Data on kidney manifestations in U1RNP-positive patients across CTD phenotypes remain limited. We aimed to characterise renal involvement using a serology-driven stratification approach.Methods: Retrospective single-centre cohort of 152 U1RNP-positive patients (University Hospital of Cologne, 2010–2023). Patients were stratified into four serological groups: isolated U1RNP (Sm−/dsDNA−, n=70; G1), U1RNP+Sm (Sm+/dsDNA−, n=15; G2), U1RNP+dsDNA (Sm−/dsDNA+, n=45; G3), and U1RNP+Sm+dsDNA (Sm+/dsDNA+, n=22; G4). Renal involvement was defined as microalbuminuria without another identifiable cause (mild) or macroalbuminuria/histologically confirmed nephritis (moderate to severe). Comparisons used Kruskal–Wallis, χ², Fisher's exact tests with Bonferroni correction (α=0.05, SPSS v31.0).Results: The cohort was 85.5% female, mean age at diagnosis of 33 years. Serological grouping strongly correlated with clinical phenotype: isolated U1RNP was associated with MCTD/UCTD (88.5%), while U1RNP+Sm+dsDNA comprised mainly SLE (86.4%). Severe renal manifestations occurred in 3.0% (G1), 40.0% (G2), 25.0% (G3), and 63.6% (G4) (p<0.001). Post-hoc comparisons confirmed significant differences between G1 vs. G2 (p=0.002), G1 vs. G3 (p=0.007), G1 vs. G4 (p<0.001), and G3 vs. G4 (p=0.014), indicating that anti-Sm and anti-dsDNA co-positivity independently contribute to renal risk. CKD prevalence increased from 13.0% (G1) to 63.6% (G4, p<0.001), with five patients requiring dialysis. Among 25 biopsied patients, membranous LN (class V) was the most frequent finding (13 cases), often combined with other classes. Proliferative LN occurred exclusively in anti-dsDNA-positive patients, while the U1RNP+Sm+dsDNA group showed the broadest LN spectrum. Neither anti-U1RNP subtype (RNP-70, RNP-A, RNP-C) nor antibody titres (ANA, anti-dsDNA) were associated with renal involvement.Conclusion: In U1RNP-positive patients, renal risk increases with serological complexity. Co-positivity with anti-Sm and/or anti-dsDNA is key determinant of renal manifestations, whereas isolated U1RNP positivity is rarely nephritogenic. These findings suggest accompanying autoantibody constellations rather than U1RNP alone drive renal disease. A serology-based approach may improve renal risk identification in this heterogeneous population. Pettersson I Wang G Smith EI Wigzell H Hedfors E Horn J Sharp GC The use of immunoblotting and immunoprecipitation of (U) small nuclear ribonucleoproteins in the analysis of sera of patients with mixed connective tissue disease and systemic lupus erythematosus. A cross-sectional, longitudinal study 1986 Arthritis Rheum 986-96 Pettersson I, Wang G, Smith EI, Wigzell H, Hedfors E, Horn J, Sharp GC. The use of immunoblotting and immunoprecipitation of (U) small nuclear ribonucleoproteins in the analysis of sera of patients with mixed connective tissue disease and systemic lupus erythematosus. A cross-sectional, longitudinal study. Arthritis Rheum. 1986 Aug;29(8):986-96. DOI: 10.1002/art.1780290807 http://dx.doi.org/10.1002/art.1780290807 Sharp GC Irvin WS Tan EM Gould RG Holman HR Mixed connective tissue disease--an apparently distinct rheumatic disease syndrome associated with a specific antibody to an extractable nuclear antigen (ENA) 1972 Am J Med 148-59 Sharp GC, Irvin WS, Tan EM, Gould RG, Holman HR. Mixed connective tissue disease--an apparently distinct rheumatic disease syndrome associated with a specific antibody to an extractable nuclear antigen (ENA). Am J Med. 1972 Feb;52(2):148-59. DOI: 10.1016/0002-9343(72)90064-2 http://dx.doi.org/10.1016/0002-9343(72)90064-2 0 0 0 0