Thereafter, several studies on Parkinson’s disease utilized AAV2 to target different pathways of dopamine production, such as glutamic acid decarboxylase (GAD) into the subthalamic nucleus, aromatic L-amino acid decarboxylase (AADC) into the putamen and, also genes linked to neuronal growth such as GDNF and neurterin. This evidence concerns the gene DDC and Parkinson disease.