According to this hypothesis, mutations in genes involved in lysosomal system have been identified in several forms of PD, such as ATP13A2 and GBA, the gene encoding for glucocerebrosidase 1, a hydrolase that catalyzes the metabolism of glucosylceramide and whose loss of function represents one of the main genetic risk factor for PD (Aharon-Peretz et al., 2004). Here, GBA1 is linked to Parkinson disease.