GBA1 and Parkinson disease: Among the genes linked to heritable monogenic PD, mutations in the α-synuclein gene SNCA (PARK1/4) [5] and the leucine-rich repeat kinase 2 gene LRRK2 (PARK8) [6] are accountable for autosomal-dominant PD forms, while mutations in PINK1 (PTEN-induced putative kinase 1; PARK6) [7], Parkin (PARK2) [8], protein deglycase DJ-1 (PARK7) [9], ATP13A2 (PARK9) [10] and β-glucocerebrosidase (GBA) [11] are responsible for an autosomal recessive mode of inheritance.