A Phase 3 Study to Evaluate the Efficacy and Safety of Efgartigimod IV in Patients With Acetylcholine Receptor Binding Antibody Seronegative Generalized Myasthenia Gravis

The primary purpose of this study is to measure the efficacy and safety of efgartigimod intravenously (IV) compared to placebo in participants with Acetylcholine Receptor Binding Antibody (AChR-Ab) seronegative Generalized Myasthenia Gravis (gMG). Other objectives are to assess long-term efficacy, safety, and tolerability of efgartigimod. Study will consist of: * Screening * Part A: participants will be randomized to receive either efgartigimod IV or placebo * Part B: participants completing part A will receive open-label efgartigimod IV