Inclusion Criteria:
1. Confirmed diagnosis of GAN disease by:
1. Genomic DNA mutation analysis demonstrating homozygous or compound heterozygous, pathogenic and/or confirmed pathogenic variants in the GAN gene;
2. Clinical history or symptoms to ANS dysfunction.
2. Previously treated with IT AAV/GAN and completion of 5 year follow up prior to enrollment.
3. Parents/l LAR willing to accompany the participant to all study visits and who will provide consent for their child's participation.
4. Subject able to comply with all protocol requirements and procedures.
5. Up to date on childhood vaccinations according to Centers for Disease Control (CDC) guidelines. Annual influenza and COVID-19 vaccinations are highly recommended.
6. Female participants of child-bearing potential must have a negative urine and/or negative serum pregnancy test at screening/baseline; (a) Female participants must agree to use an effective form of birth control during study participation.
Exclusion Criteria:
1. Inability to participate in study procedures (as determined by the site investigator).
2. Inability to be safely sedated in the opinion of the clinical anesthesiologist.
3. Concomitant illness or requirement for chronic drug treatment that in the opinion of the Principal Investigator (PI) creates unnecessary risks for gene transfer.
4. The presence of significant non-GAN related CNS impairment or behavioral disturbances that would confound the scientific rigor or interpretation of results of the study.
5. Have received an investigational drug within 30 days prior to screening or plan to receive an investigational drug (other than this gene therapy) during the study.
6. Currently participating in another interventional (drug/device) clinical trial.
7. Experienced an SAE (serious adverse event) related to scAAV9/JeT-GAN while participating in the first GAN IT study.
8. Contraindication to scAAV9/JeT-GAN or any of its ingredients.
9. Contraindication to any of the immune suppression medications used in this study.
10. Clinically significant abnormal laboratory values (GGT, ALT, and AST, or total bilirubin \> 3 × ULN, creatinine ≥ 1.5 mg/dL, hemoglobin \[Hgb\] \< 6 or \> 20 g/dL; white blood cell \[WBC\] \> 20,000 per cmm) prior to gene replacement therapy
View Inclusion and Exclusion Criteria at ClinicalTrials.gov