PPT1 and neuronal ceroid lipofuscinosis: Furthermore, signs of synaptic dysfunction (reduction in synaptic vesicle number) and degeneration have been demonstrated in PPT1 deficient neurons in vitro[49], and synaptic pathology (redistribution of SNARE complex and aggregates of Syp/SNAP25) occurs early on in disease progression in the congenital form of NCL [50].