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El Kamouni H, S Jalaledin D, Albert A, Hoa S, Vo C, Bourré-Tessier J, Rich É, Goulet JR, Koenig M, Pérez G, Choi MY, Troyanov Y, Satoh M, Fritzler MJ, Senécal JL, Landon-Cardinal O. Anti-SMN autoantibodies in mixed connective tissue disease are associated with a severe systemic sclerosis phenotype. RMD Open 2023; 9:e003431. [PMID: 37797966 PMCID: PMC10551952 DOI: 10.1136/rmdopen-2023-003431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Accepted: 08/14/2023] [Indexed: 10/07/2023] Open
Abstract
OBJECTIVES The survival of motor neuron (SMN) complex has an essential role in the assembly of small nuclear ribonucleoproteins (RNP). Recent reports have described autoantibodies (aAbs) to the SMN complex as novel biomarkers in anti-U1RNP+ myositis patients. The aim of this study was to compare phenotypic features of anti-U1RNP+ mixed connective tissue disease (MCTD) patients with and without anti-SMN aAbs. METHODS A retrospective MCTD cohort was studied. Addressable laser bead immunoassay was used to detect specific anti-SMN aAbs with <300 mean fluorescence intensity (MFI) as normal reference range, 300-999 MFI as low-titre and ≥1000 MFI as high-titre positivity. Comparison of clinical features between anti-SMN+ and anti-SMN- subgroups used two-tailed Fisher's exact test, and logistic regression analyses. RESULTS Sixty-six patients were included. Median age at MCTD diagnosis was 40.6 years, and duration of follow-up was 12 years. Based on the highest available titre, 39 (59%) were anti-SMN+: 10 (26%) had low titre and 29 (74%) had high titre. Anti-SMN+ patients had a higher frequency of fingertip pitting scars (anti-SMN+ 23% vs anti-SMN- 4%, p=0.04), lower gastrointestinal (GI) involvement (26% vs 4%, p=0.04), and myocarditis (16% vs 0%, p=0.04). The combined outcome of pitting scars and/or lower GI involvement and/or myositis and/or myocarditis was highest among high-titre anti-SMN+ patients: adjusted OR 7.79 (2.33 to 30.45, p=0.002). CONCLUSIONS Anti-SMN aAbs were present in 59% of our MCTD cohort. Their presence, especially at high-titres, was associated with a severe systemic sclerosis (scleroderma) phenotype including myositis, myocarditis and lower GI involvement.
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Affiliation(s)
- Hajar El Kamouni
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
- Division of Rheumatology, Hôpital de la Cité-de-la-Santé, Laval, Quebec, Canada
| | - Darya S Jalaledin
- Division of Internal Medicine, Centre hospitalier de l'Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | - Alexandra Albert
- Clinique Multidisciplinaire de Neuville, Neuville, Quebec, Canada
| | - Sabrina Hoa
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Caroline Vo
- Division of Rheumatology, Hôpital Charles-LeMoyne, Greenfield Park, Quebec, Canada
| | - Josiane Bourré-Tessier
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Éric Rich
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Jean-Richard Goulet
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Martial Koenig
- Division of Internal Medicine, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Gemma Pérez
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - May Y Choi
- Department of Medicine, University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada
| | - Yves Troyanov
- Division of Rheumatology, Hôpital du Sacré-Coeur de Montréal, Montreal, Quebec, Canada
| | - Minoru Satoh
- Department of Medicine, Kitakyushu Yahata-Higashi Hospital, Kitakyushu, Japan
- Department of Human, Information and Sciences, University of Occupational and Environmental Health, Kitakyushu, Japan
| | - Marvin J Fritzler
- Department of Medicine, University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada
| | - Jean-Luc Senécal
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Océane Landon-Cardinal
- Division of Rheumatology, Centre hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
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