The primary objective of this dose-finding study is to evaluate the safety, tolerability and pharmacodynamics of single dose of INS1202 via IT administration in participants ≥ 18 to <80 years of age with ALS who carry superoxide dismutase type 1 (SOD1) mutations or harbor no known ALS-related genetic mutation.

Key Inclusion Criteria: -

• Participant with body mass index (BMI) ≥18 kilograms per square meter (kg/m^2).
• Participant with symptomatic ALS as diagnosed by Gold Coast diagnostic criteria.
• Sporadic ALS cohorts: Negative testing for known monogenic mutations associated with familial ALS.
• SOD1-ALS (Cohorts 2 and 3 only): Confirmed pathogenic SOD1 mutation, with negative testing for other genetic mutations associated with familial ALS.
• Any polymorphism or mutation in the coding region will require additional review by the Sponsor to determine compatibility with the study intervention.
• Baseline ALSFRS-R ≥ 24.
• ALS disease duration ≤ 42 months.

Key Exclusion Criteria: -

• Previous treatment for ALS with cellular or gene therapies.
• Any investigational medication or treatment (for ALS or other condition).

Note: Other protocol-defined inclusion/exclusion criteria may apply.