Importantly, lysosomal cathepsins do not only degrade αSyn, but also other substrates, including numerous aggregation-prone proteins associated with numerous neurodegenerative diseases: (i) amyloid-beta precursor protein (APP) and (ii) microtubule-associated protein tau that are both related to Alzheimer’s disease [67–69], (iii) huntingtin related to Huntington’s disease [70, 71], and (iv) prion protein related to the prion protein diseases [72, 73]. Here, APP is linked to juvenile Huntington disease.