GBA1 and Parkinson disease: Monogenic PD patients with mutations in the genes leucine-rich repeat kinase 2 (LRRK2) (Khan et al. 2005; Healy et al. 2008), PTEN-induced putative kinase 1 (PINK1) (Ferraris et al. 2009), vacuolar protein sorting 35 (VPS35) (Struhal et al. 2014), glucocerebrosidase (GBA) (Alcalay et al. 2012) showed similar changes in UPSIT scores to those with idiopathic PD, but patients with Parkin (Khan et al. 2004; Malek et al. 2016) mutations showed normal olfactory function.