Original article Autoantibodies to Mi-2 alpha and Mi-2 beta in patients with idiopathic inflammatory myopathy Michaelin Richards 1 , Ignacio Garcı´a-De La Torre 2 , Yelitza C. Gonza ´ lez-Bello 3 , Mo ´ nica Va ´ zquez-Del Mercado 4 , Lilia Andrade-Ortega 5 , Gabriel Medrano-Ramı´rez 6 , Jose Eduardo Navarro-Zarza 7 , Marco Maradiaga-Cecen ˜a 8 , Esthela Loyo 9 , Armando Rojo-Mejı´a 10 , Graciela Go ´ mez 11 , Andrea Seaman 1 , Marvin J. Fritzler 12 , Martial Koenig 13 and Michael Mahler 1 Abstract Objectives. The objective of this study was to compare the results obtained from different assays for the detection of anti-Mi-2 antibodies, which are important markers in the diagnosis of DM. Methods. The study included 82 patients (68 females/14 males), most of whom had DM (n = 57), followed by PM (n = 16) and juvenile DM (n = 9). All samples were tested using a novel particle-based multi-analyte technology (PMAT) (Inova Diagnostics, research use only) in parallel with a line immunoassay (LIA: Euroimmun). To assess clinical specificity for the PMAT assay, a total of 775 disease and healthy controls were tested. Results. 29 samples were positive by at least one test for anti-Mi-2 antibodies. Of those, 24 were Mi-2b LIA+, five were Mi-2a LIA+ and 23 Mi-2 PMAT+. The comparison shows varying agreement between the different methods (kappa 0.270.77). When LIA results were used as reference for receiver operating characteristics analysis, high area under the curve values were found for both PMAT vs LIA Mi-2a and LIA Mi-2b. When analysing the results in the context of the myositis phenotype, PMAT associated closest with the DM phenotype. In the control group, 3/775 controls (all low levels) were anti-Mi-2+ resulting in a sensitivity and specificity of 28.1% and 99.6%, respectively. Conclusion. Overall, good agreement was found between LIA and PMAT for anti-Mi-2 antibodies, which is important for the standardization of autoantibodies. Anti-Mi-2b antibodies measured by PMAT tend be more highly associated with the clinical phenotype of DM. Key words: autoantibodies, myositis, DM, anti-Mi-2 antibodies, immunoassay Rheumatology key messages . Isoform Mi-2b appears to be sufficient for the detection of anti-Mi-2 antibodies in myositis. . Diagnostic platform has an impact on the accuracy of the results. . Results derived from novel particle-based multi-analyte technology agree well with the DM phenotype and immunofluorescence pattern. 1 Research and Development, Inova Diagnostics, San Diego, CA, USA, 2 Departamento de Inmunologı´a y Reumatologı´a, Hospital General de Occidente and University of Guadalajara, Guadalajara, Jalisco, 3 Departamento de Reumatologı ´a Centro de Estudios, de Investigacio ´n Ba ´sica y Clı´nica, S.C., Guadalajara, Jalisco, 4 Servicio de Reumatologı´a, Hospital Civil de Guadalajara ‘Dr Juan I. Menchaca’, Guadalajara, Jalisco, 5 Departamento de Reumatologı´a Centro Me ´ dico Nacional 20 de Noviembre, ISSSTE, 6 Departamento de Reumatologı´a Hospital General de Me ´ xico, ‘Dr Eduardo Liceaga’, Me ´ xico City, 7 Departamento de Reumatologı ´a Hospital General, ‘Dr Raymundo Abarca Alarco ´ n’, Chilpancingo, Guerrero, 8 Departamento de Reumatologı´a Hospital General de Culiaca ´ n, ‘Dr Bernardo Gastelum’, S.S., Culiaca ´ n, Sinaloa, Mexico, 9 Servicio de Reumatologı ´a e Inmunologı´a, Clı´nica Hospital Regional Universitario ‘Jose ´ Ma. Cabral y Ba ´ ez’, Santiago, Rep. Dominicana, 10 Departamento de Reumatologı´a, Clı´nica San Pablo, Surco, Lima, Peru ´, 11 Departamento de Inmunologı´a, Instituto de Invest. Me ´ dicas, Alfredo Lanari, Universidad de Buenos Aires, Argentina, 12 Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada and 13 Department of Medicine, Universite ´ de Montre ´ al, Montreal, QC, Canada Correspondence to: Michael Mahler, Inova Diagnostics, 9900 Old Grove Road, San Diego, CA 32131-1638, USA. E-mail: mmahler@inovadx.com; m.mahler.job@web.de Submitted 7 December 2018; accepted 19 February 2019 ! The Author(s) 2019. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For permissions, please email: journals.permissions@oup.com RHEUMATOLOGY Rheumatology 2019;58:16551661 doi:10.1093/rheumatology/kez092 Advance Access publication 1 April 2019 CLINICAL SCIENCE Downloaded from https://academic.oup.com/rheumatology/article/58/9/1655/5425280 by guest on 01 August 2022