Objective Patients with myasthenia gravis without acetylcholine receptor (AChR) or muscle-specific kinase (MuSK) antibodies detected by radioimmunoprecipitation assays (RIAs) are classified as seronegative myasthenia gravis (SNMG). Live cell-based assays (l-CBAs) can detect additional antibodies to clustered AChR, MuSK and low-density lipoprotein receptor-related protein 4 (LRP4), but positivity rates are variable and both clinical relevance and utility of CBA platforms remain unclear.
Methods Sera from 82 patients with SNMG were tested by l-CBAs. Human embryonic kidney cells were transfected to individually express clustered AChR, MuSK or LRP4; or transfected to jointly express both clustered adult AChR and MuSK. Sera from 30 and 20 patients positive by RIA for AChR or MuSK antibodies were used as comparators.
Results 53 of 82 (72%) patients with SNMG had generalised and 29 (28%) had ocular disease. The clustered AChR CBA detected antibodies in 16 of 82 patients (19.5%; including 4 patients with solely fetal AChR antibodies), while 7 of 82 (8.5%) patients had MuSK antibodies. A novel exploratory combined adult AChR-MuSK l-CBA efficiently detected all these antibodies in a subset of the SNMG cohort. No LRP4 antibodies were identified. Overall, patients with SNMG with clustered AChR antibodies, CBA-positive MuSK-MG or triple seronegative were younger, had less severe disease than patients with RIA-positive MG and had a better clinical outcome when immunotherapy was started soon after disease onset, although the time interval from onset to immunotherapy was not different when compared with patients with RIA-positive MG.
Conclusion Around one-third of patients with SNMG had AChR or MuSK antibodies by l-CBAs, which were efficiently detected with a combined l-CBA. The results in this large and unselected cohort of patients with MG demonstrate the diagnostic usefulness of performing CBAs and the importance of making these tests more widely available.
Data availability statement
Data are available upon reasonable request.
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Contributors Study concept and design—VD and AE. Acquisition of data—VD, GS, GM, MW, LJ, SF, TS, RI and AE. Analysis and interpretation of data—VD, GS, GM, MW, LJ, SF, TS, PW, SRI, AV and AE. Drafting of the manuscript—VD and AE. Critical revision of the manuscript for important intellectual content—VD, GS, PW, SRI, AV and AE. Study supervision—PW, SRI, AV and AE. VD and AE act as guarantors.
Funding SRI is supported by the Medical Research Council (MR/V007173/1), Wellcome Trust (104079/Z/14/Z), BMA Research Grants–2013 Vera Down grant, Epilepsy Research UK (P1201) and by the Fulbright UK-US commission (MS-Research Society Award). This research was funded in whole, or in part, by the Wellcome Trust (grant number 104079/Z/14/Z). VD is supported by the Myasthenia Gravis Rare Disease Network–MGNet, a member of the Rare Disease Clinical Research Network Consortium (RDCRN) NIH U54 NS115054. All RDCRN consortia are supported by the network’s Data Management and Coordinating Center (DMCC) (U2CTR002818). Funding support for the DMCC is provided by the National Center for Advancing Translational Sciences (NCATS) and the National Institute of Neurological Disorders and Stroke (NINDS). Part of the work was supported by the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre (BRC).
Disclaimer The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.
Competing interests AV and the University of Oxford held a patent for detection of MuSK antibody assays (expired 2020), licensed to Athena Diagnostics; AV received a proportion of royalties. SRI and PW are co-applicants and receive royalties on patent application WO/2010/046716 entitled ‘Neurological Autoimmune Disorders’ (the patent has been licensed for the development of assays for LGI1 and other VGKC-complex antibodies) and have filed two other patents regarding autoantibody diagnostic algorithms.
Provenance and peer review Not commissioned; externally peer reviewed.
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