Inclusion Criteria:  Confirmation of C9orf72 mutation Diagnosis of ALS by revised El Escorial criteria Time since onset of muscle weakness due to ALS ≤36 months at the time of the Screening Visit Slow Vital Capacity (VC) ≥50% of predicted capacity at the time of the Screening Visit If taking riluzole, must be on a stable dose of riluzole for at least 30 days prior to the Screening Visit. Riluzole naive participants are allowed. If taking edaravone, must have completed at least one cycle of edaravone prior to the Screening Visit and plan to continue edaravone during the study. Edaravone naive participants are allowed. Females must not be pregnant, breastfeeding or planning to conceive within the study period. Males must agree to use acceptable contraception Capable of providing informed consent at the Screening visit and complying with study procedures throughout the study  Exclusion Criteria:  Clinically significant, unstable, medical condition (other than ALS) Clinically significant heart disease, liver disease or kidney disease Cognitive impairment or dementia Current uncontrolled hypertension History of unresolved cancer Any experimental gene therapy Any experimental vaccine (any vaccine against COVID-19 either approved or administered under an Emergency Use Authorization is allowed)