Studies in adults with Parkinson disease have shown that the intraputaminal infusion of the adeno-associated virus type 2 (AAV2) vector-mediated delivery of the human AADC gene increases AADC enzymatic activity, with good safety and tolerability profiles.13, 14, 15 Because the main symptoms of AADC deficiency include reduced brain dopamine levels and motor function impairments, this disease would be a promising candidate for a gene therapy approach similar to that used in Parkinson disease. This evidence concerns the gene DDC and aromatic L-amino acid decarboxylase deficiency.