In patients affected by Parkinson's disease (PD), the 8-year follow-up on ProSavin, an LV delivering key enzymes of the dopamine biosynthetic pathway (tyrosine hydroxylase, aromatic l-amino acid decarboxylase, and guanosine 5′-triphosphate cyclohydrolase 1), documented an improvement of the “off” time in 8/15 treated patients. Here, TH is linked to Parkinson disease.