PPT1 and neuronal ceroid lipofuscinosis: PPT1 protein is a small glycoprotein involved in the catabolism of lipid-modified proteins during lysosomal degradation, and mutations in the PPT1 gene cause infantile neuronal ceroid lipofuscinosis 1 (CLN1; OMIM #256730) and neuronal ceroid lipofuscinosis 4 (CLN4; OMIM #204300).