Sponsor decision to terminate program

This study will evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics (PD), immunogenicity, and efficacy of subcutaneous (SC) ALXN1830 in adults with generalized myasthenia gravis (gMG).

Participants have the option to enroll in an Open-label Extension (OLE) Period to receive ALXN1830 up to 58 weeks (including follow-up period).

Key Inclusion Criteria:

• Diagnosis of myasthenia gravis.
• Positive serologic test for anti-acetylcholine receptor antibodies.
• Myasthenia Gravis Foundation of America Clinical Classification Class II to IV at Screening.
• MG-ADL profile must be ≥ 5.
• Participants receiving stable treatment with azathioprine; other immunosuppressive therapies.
• Total IgG level at Screening ≥ 600 milligrams/deciliter.

Key Exclusion Criteria:

• History of thymectomy, thymomectomy, or any other thymic surgery within 12 months prior to Screening.
• Any untreated thymic malignancy, carcinoma, or thymoma.
• Intravenous immunoglobulin within the 6 weeks, and/or use of plasmapheresis/plasma exchange prior to randomization (Day 1).
• Use of rituximab within the 3 months (90 days) prior to Screening.
• Participants who have received previous treatment with any biological agent or other anti-neonatal fragment crystallizable receptor therapy within 5 half-lives or 90 days after last dose (whichever is longer).
• Known medical or psychological condition(s) or risk factor that, in the opinion of the Investigator, might interfere with the participant's full participation in the study, pose any additional risk for the participant, or confound the assessment of the participant or outcome of the study.