Seronegative Myasthenia Gravis - Efgartigimod IV

Evidence of signed and dated informed consent document(s) indicating that the subject has been informed of all pertinent aspects of the trial. Subjects must be willing and able to comply with the protocol, complete study assessments, and return for follow-up visits.

Male or female subjects ≥ 18 years old.

Diagnosis of SN MG defined as: (a) clinical syndrome consistent with a diagnosis of MG, and not otherwise explained by another condition, (b) abnormal neuromuscular transmission test results demonstrated by single-fiber electromyography or repetitive nerve stimulation; and (c) negative serologic test for anti-AChR and anti- MuSK antibodies as confirmed at screening, (d) limited, if any, response to therapy with immunotherapy and/or antiacetylcholinesterase (AChE) treatment. Further testing for low affinity antibodies to rapsyn-clustered AChR by cell-based assays will be done at baseline and the results included as part of subgroup analysis. All patients will have a negative genetic test for congenital myasthenic syndromes by history or at baseline to exclude the possibility of congenital myasthenic syndrome mimicking SN MG.

MGFA Clinical Classification Class II, III, or IV at the time of screening and baseline.