• Male or female subjects age 18 - 80 years, inclusive;
• Diagnosis of familial or sporadic ALS as defined by the El Escorial-Revised (2000) research diagnostic criteria for ALS [clinically definite, clinically probable, probable-laboratory-supported];
• ALS onset of ≤18 months from first clinical signs of weakness prior to screening;
• If currently using riluzole, subject must be on a stable dose for at least 30 days prior to initiation of study drug;
• If currently using edaravone, subject should have completed at least 14 days of their initial treatment cycle prior to initiation of study drug;
• Last documented pulmonary function test result (i.e., slow vital capacity or forced vital capacity) must be greater than or equal to 70% predicted;;
• Able to swallow study medication capsules;
• No known allergies to the study drug or its excipients;
• Received pneumococcal vaccine within 6 years prior to starting clinical trial.

Major

• ALSFRS-R score of ≤1 on more than one item in the assessment's individual components;
• Currently diagnosed with a clinically significant psychiatric disorder or dementia that would preclude evaluation of symptoms;
• Currently use or treated with parenteral (intramuscular or intravenous) high dose (>25 mg/week) Vitamin B12 within 30 days prior to study drug administration;
• Poor peripheral venous access that will limit the ability to draw blood as judged by the Investigator;
• Currently participating, or has participated in a study with an investigational or marketed compound or device within 30 days or 5 half-lives, whichever is shorter, prior to signing the informed consent;
• Use of tracheostomy or >22/24-hour ventilatory support.