LRRK2 and Parkinson disease: Several widely tested biomarkers have been investigated intensively for several decades to diagnose PD with high accuracy, including α-synuclein (α-syn), protein deglycase (DJ-1), Leucine-rich repeat kinase 2 (LRRK2), amyloid-beta, apolipoprotein A1 (ApoA1), dopamine (DA), and glutathione [9,10,11].