This study is to continue Long-Term Follow-Up of Patients who were previously treated with AXO-AAV-GM2 Gene Therapy as treatment for Tay-Sachs or Sandhoff Disease to follow the subjects through 5 years after their initial gene therapy treatment.

Subjects will be contacted bi-annually for a total of five years following the administration of AXO-AAV-GM2 for the collection of clinical information, especially pertaining to de novo cancer, neurologic, rheumatologic, and hematologic/immunologic disorders. This will be done to comply with FDA Recommendations and NIH Guidelines for long-term follow-up for research involving gene therapy with AAV Vectors.

Inclusion Criteria:

• Subjects who were previously enrolled in the study "A Two-Stage Dose-Escalation Study to Evaluate the Safety and Efficacy of Bilateral Intraparenchymal thalamic and intracisternal/Intrathecal Admin of AXO-AAV-GM2 in Tay-Sachs or Sandhoff Disease."

Exclusion Criteria:

• Subjects who were not previously enrolled under the initial protocol.

Subjects with Tay-Sachs or Sandhoff Disease who were previously treated with AXO-AAV-GM2