SLC6A3 and Parkinson disease: Recombinant human platelet‐derived growth factor‐BB (rhPDGF‐BB) reduced PD symptoms and increases dopamine transporter binding in animal models.[260] In a phase I clinical trial rhPDGF‐BB was injected intracerebroventricularly into 12 PD patients at the maximum dose of 5 μg per day for 12 days.