CTSS and neurodegenerative disease: As α-syn, TDP-43 and tau are all intrinsically disordered proteins that are found in disease inclusions and whose mutations are causally linked to neurodegeneration [64], understanding the full metabolism of α-syn, TDP-43 and tau, including the specifics sites of proteolytic cleavage and the cathepsins responsible, holds particular relevance in neurodegenerative disease.