For example, direct injection of an AAV2‐delivered transgene using a surgical approach similar to the implanting of deep brain stimulation electrodes was sufficient for a Phase II trial of a gene therapy for Parkinson's disease to successfully achieve its efficacy endpoint.29 An ongoing trial (NCT03065192) of AAV2‐mediated delivery of DNA encoding aromatic l‐amino acid decarboxylase (AADC) for Parkinson's disease is using a direct injection approach involving multiple infusions along a posterior trajectory through the striatum from an occipital entry point. Here, DDC is linked to Parkinson disease.