Parkinson’s disease (PD) is a progressive disease characterized by loss of dopaminergic neurons in the substantia nigra, which lead to motor symptoms. Aromatic-L-amino-acid decarboxylase (AADC) converts levodopa into dopamine and glial cell line-derived neurotrophic factor (GDNF) promotes the survival, growth and regeneration of dopaminergic neurons. VGN-R09b is an adeno-associated viral vector (AAV)-based AADC and GDNF combination gene therapy that is delivered to the striatum for the treatment of PD.