PER2 and Parkinson disease: Other than alpha-synuclein, some genes such as ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1) promoter, ATP13A2 promoter, Parkin (PARK2) gene, and other clock genes such as period circadian regulator (PER1), period circadian regulator-2, cryptochrome circadian regulator-1, cryptochrome circadian Regulator-2, neuronal PAS domain protein 2 (NPAS2), and brain and muscle ARNT-like 1 (BMAL1) have also been measured in genomic DNA isolated from PD patients to check their role in PD.