CTSD and neuronal ceroid lipofuscinosis: Human postmortem studies with brains from early-onset neuronal ceroid-lipofuscinosis patients showed the accumulation of α-synuclein aggregates.46 Furthermore, in an α-synuclein transgenic fly model, depletion of CTSD accelerated the formation of α-synuclein aggregates and the associated pathogenic phenotypes, such as accumulation of numerous vacuoles and disruption of the retina structure.46 These results indicate that CTSD is critical for maintaining the levels of α-synuclein in check, and therefore, reduced expression of CTSD might increase the risk of synucleinopathies.