A Study to Evaluate the Safety and Efficacy of Nizubaglustat (AZ-3102) in Patients With GM2 Gangliosidosis or Niemann-Pick Type C Disease

Inclusion Criteria: * Cohort 1 (NPC and GM2 patients): * Have been randomized into Phase 2 Study AZA-001-5A2-01. OR Cohort 2 (NPC patients): * Be male or female aged ≥12 years * Have a genetically-confirmed diagnosis of NPC disease * Have received full-dose Miglustat treatment for at least 12 months and experienced disease stabilization or worsening with treatment over the 2 previous clinic visits. Patients experiencing clinical improvement with Miglustat over the preceding 3 months should not be considered for this study. * Wish to change treatment to Nizubaglustat for their NPC disease. * Participants from Phase 2 Study AZA-001-5A2-01 (RAINBOW) who transitioned to Miglustat may be eligible for Cohort 2 if they meet all other criteria. Participation is supported and deemed beneficial by the Principal Investigator. Be willing and able to be evaluated for all protocol assessments. The participant, parent, and/or legal guardian can read, understand, and sign the informed consent form. Where appropriate, assent will also be sought for participants who have not reached the age of majority. Exclusion Criteria: * A positive serum pregnancy test (only tested for women of childbearing potential). * Female planning to breastfeed during the study. * Any medical event/condition that prevents participation in the study based on the judgment of the Principal Investigator. * Participation in another interventional or non-interventional study or early access program.