CTSD and neurodegenerative disease: Several genomic variants of CTSD, like coding missense mutations, seem to be related to neurodegenerative diseases, such as neuronal ceroid lipofuscinosis (NCL), Alzheimer’s disease (AD), and PD, all progressive disorders involving the central nervous system (CNS) and aggregation of misfolded proteins (Siintola et al., 2006; Steinfeld et al., 2006; Fritchie et al., 2009; Hersheson et al., 2014; Robak et al., 2017).