GBA1 and Parkinson disease: Homozygous loss of function mutations in GBA cause the lysosomal storage disorder GD (Montfort et al., 2004; Hruska et al., 2008), but carrying a single mutant allele is also a major risk factor for a group of neurodegenerative disorders termed synucleinopathies (Lwin et al., 2004; Alcalay et al., 2014; Shiner et al., 2021), which includes PD and dementia with Lewy bodies (DLB).