ATP13A2 and Parkinson disease: Genome-wide association studies have established 26 PD risk loci to date and, among the different PARK genes, those which encode α-synuclein (PARK1/4), Parkin (PARK2), PINK1 (phosphatase and tensin homolog (PTEN)-induced kinase 1—PARK6), DJ-1 (PARK7), LRRK2 (PARK8), and ATP13A2 (PARK9) have been deeply investigated.