SMPD1 and metachromatic leukodystrophy: Additionally, SMPD1 (acid sphingomyelinase, deficient in Niemann Pick type A, B), ASAH1 (acid ceramidase, deficient in Farber’s disease and spinal muscular atrophy with progressive myoclonic epilepsy), ARSA [arylsulfatase A, deficient in metachromatic leukodystrophy (MLD)] and GALC [lysosomal galactosylceramidase, deficient in Krabbe’s disease (KD)] are also associated with vulnerability to develop adult onset neurodegenerative disorders, particularly PD (Smolders and Van Broeckhoven, 2020).