GBA1 and Parkinson disease: As mentioned in Section 1, variants of GBA2, coding for the non-lysosomal glucosylceramidase, an enzyme that catalyzes the hydrolysis of GlcCer to glucose and ceramide, have been associated with spastic paraplegia and SA, while variants of GBA, coding for the lysosomal glucosylcermidase have been associated with Gaucher’s disease and Parkinson’s disease [21].