TPP1 and frontotemporal dementia: For example, mutations in CLN1 (palmitoyl-protein thioesterase 1; PPT-1) and CLN2 (tripeptidyl-peptidase 1; TPP-1) are also associated with neuronal loss in the substantia nigra in adults (Nijssen et al., 2003), early onset frontotemporal dementia (Jeung et al., 2015) and juvenile onset forms of ataxia (SCA type 7; SCAR7; Sun et al., 2013).