GBA1 and Parkinson disease: In contrast to PD, which is linked to a deficiency in lysosomal GBA activity, loss-of-function mutations in GBA2, a microsomal and non-lysosomal GBA, are associated with an autosomal dominant form of SCA (Votsi et al., 2014; Sultana et al., 2015; Synofzik and Schüle, 2017) and an autosomal recessive form of HSP featuring cognitive impairment (Martin et al., 2013; Sultana et al., 2015; Yang et al., 2016).