2023 American Academy of Neurology Abstract Website

Objective:

To refine the serological characterization of patients with seronegative myasthenia gravis (SNMG) and explore novel disease-specific autoantibody reactivities.

Background:

MG is characterized by a detrimental humoral response against key proteins on the neuromuscular junction, including the acetylcholine receptor (AChR) and muscle-specific tyrosine kinase (MuSK). In about 10% of MG patients, defined as seronegative, a lack of detectable autoantibodies by radioimmunoassay hampers a prompt diagnosis and restricts eligibility for clinical trials and payers’ reimbursement for certain therapies. In variable proportions of SNMG patients, autoantibodies can be detected by cell-based assays (CBA). However, data on CBA positivity rates in the U.S. are lacking. Moreover, the prevalence of low-density lipoprotein receptor-related protein 4 (LRP4) autoantibodies, and the presence of autoantibodies against yet unidentified muscle autoantigens, remain uncertain in SNMG.

Design/Methods:

Serum or plasma samples from SNMG patients in two U.S. academic centers were tested by clustered AChR, MuSK or LRP4 CBA using flow cytometry. A B cell culturing approach that allows for in vitro differentiation of B cells into antibody-secreting cells was employed to identify circulating antigen-specific B cells and generate recombinant monoclonal antibodies. Rapid extracellular antigen profiling (REAP), a high-throughput antibody discovery technique, was leveraged to explore novel autoantibody reactivities in SNMG patients.

Results:

Of 99 SNMG samples tested by CBA, 18 (18.2%) were positive for AChR autoantibodies; none were MuSK or LRP4 autoantibody positive. As further evidence of a positive AChR autoantibody status, circulating AChR-specific B cells were identified in a CBA-positive SNMG patient, and their specificity was validated through the isolation of a recombinant monoclonal antibody. REAP revealed potentially novel autoantibody reactivities restricted to SNMG patients.

Conclusions:

Findings from a large SNMG cohort support the clinical need to implement clustered AChR CBA testing in the evaluation of SNMG patients. Further ongoing investigations are warranted to confirm the presence of novel autoantibodies in SNMG.