SMPD1 and Parkinson disease: Alcalay et al. [78] used dried blood spots of 648 PD cases vs. 317 controls to test whether reduction in lysosomal enzymatic activity in PD is specific to GBA, measuring the activity of GBA, acid sphingomyelinase (Niemann–Pick disease types A and B), a-GAL A galactosidase A (AFD), acid alpha-glucosidase (Pompe disease), and galactosylceramidase (Krabbe disease).