A Trial to Evaluate Safety and Efficacy of a Product Named VGN-R09b in Severe AADC Deficiency

Inclusion Criteria: 1. The child patient has to be ≥18 months old and \< 8 years old, and a head circumference big enough for surgery as judged by investigator. 2. Historical diagnosis of AADC deficiency with clinical symptoms consistency, AND with Molecular genetic confirmation of homozygous or compound heterozygous mutation point of IVS6+4A\>T in DDC gene. 3. With Plasma AADC activity less than or equal to 12 pmol/min/mL. 4. Motor development at baseline \<3 months (head fully uncontrollable at baseline）, and Failed to benefit from standard medical therapy (dopamine agonists, monoamine oxidase inhibitor or related form of Vitamin B6) at discretion of investigators. 5. Parent(s)/legal guardian(s) with custody of subject must give their consent for subject to enroll in the study. 6. Parent(s)/legal guardian(s) of the subject must agree to comply with the requirements of the study, including providing disease information and support disease assessment of symptoms. Exclusion Criteria: 1. Intracranial neoplasm or any structural brain abnormality or lesion (e.g., severe brain atrophy, white matter degenerative changes), which, in the opinion of the study investigators, would confer excessive risk and/or inadequate potential for benefit. 2. Presence of other significant medical or neurological conditions that would create an unacceptable operative or anesthetic risk (including congenital heart disease, respiratory disease with home oxygen requirement, history of serious anesthesia complications during previous elective procedures, history of cardiorespiratory arrest), liver or renal failure, malignancy, or HIV positive. 3. Severe coagulopathy, or need for ongoing anticoagulant therapy. 4. clinically active infection or with severe infection within 12 weeks before screening (e.g. adenovirus or herpes virus, pneumonia, sepsis, central nervous system infection). 5. Previous stereotactic neurosurgery, or any gene/cell therapy. 6. Received live vaccination within 4 weeks. 7. Contraindication to sedation during surgery or imaging studies (PET or MRI).