PPT1 and infantile neuronal ceroid lipofuscinosis: A study of brain tissue from INCL patients and a constitutive Ppt1 knockout (Ppt1-KO) mouse model linked rapid neurodegeneration to increased apoptosis indicated by elevated levels of caspases 3 and 9 and cleaved poly-ADP ribose polymerase enzyme (PARP) (Kim et al., 2006).