Key Inclusion Criteria:

   1. A diagnosis of sporadic or familial ALS, defined by the El Escorial criteria
   (possible, laboratory-supported probable, probable, or definite ALS).

   2. ALS onset ≤ 36 months from Screening.

   3. Documented meningococcal vaccination not more than 3 years prior to, or at the time
   of, initiating study treatment.

   4. Upright slow vital capacity ≥ 65% predicted at Screening.

   5. If on riluzole, participant must be on a stable dose for 30 days; if on edaravone,
   participant must be on a stable dose for 60 days (2 cycles).

   6. Body weight ≥ 40 kilograms at Screening.

   7. Contraceptive use by men or women should be consistent with local regulations
   regarding the methods of contraception for those participating in clinical studies.

Key Exclusion Criteria:

   1. History of Neisseria meningitidis infection.

   2. Human immunodeficiency virus (HIV) infection (evidenced by HIV 1 or HIV 2 antibody
   titer).

   3. Dependence on invasive or non-invasive mechanical ventilation.

   4. Previously or currently treated with a complement inhibitor.

   5. Exposure to an investigational drug or device within 30 days of Screening or 5 half
   lives of the study drug, whichever is greater.