First in Human (FIH) Study of ALN-SOD in Adult Participants With Amyotrophic Lateral Sclerosis Associated With Mutation in the SOD1 Gene (SOD1-ALS)

Key Inclusion Criteria: 1. Weakness attributable to ALS and a SOD1 variant that has been previously described as associated with ALS or is considered likely to cause ALS, as defined in the protocol 2. Slow Vital Capacity (SVC) ≥50% predicted value based on age, gender and height, measured in upright position 3. Body Mass Index (BMI) ≤35 kg/m2 at time of screening 4. If participants are taking riluzole or edaravone, they must be on a stable dose for at least 4 weeks prior to initial dosing visit and are expected to remain at that dose until the end of the study 5. Platelet count \>50,000/microliter 6. Has normal blood pressure readings, as defined in the protocol Key Exclusion Criteria: 1. Concurrent participation in another interventional clinical trial 2. Has had a tracheostomy 3. Has dementia, as assessed by the investigator 4. Has uncontrolled psychiatric disease, including psychosis, active or recent suicidal ideation, untreated major depression, in the past 30 days 5. Has a medical history of brain or spinal disease/injury that would interfere with the Lumbar Puncture (LP) process, CSF circulation or safety assessment, as defined in the protocol 6. Presence of an implanted shunt for the drainage of CSF or an implanted Central Nervous System (CNS) catheter 7. Presents any concern to the study investigator that might confound the results of the study or poses an additional risk to the participant by their participation in the study 8. Was hospitalized (ie, \>24 hours) for any reason other than ALS within 30 days of screening 9. Has received treatment with tofersen within 6 months prior to screening NOTE: Other protocol defined inclusion / exclusion criteria apply