DRD2 and Parkinson disease: Four of the currently known genes involved in DOPA signaling, park2, pink1, DRD2 and slc6a3, whose monogenic mutations are found in early or juvenile onset PD patients [36]—were decreased in the 10 mg/kg/day group of 3-month-old mice, while synuclein levels were not altered, as happens in Parkinsonians.