PPT1 and infantile neuronal ceroid lipofuscinosis: Neuronal ceroid lipofuscinosis type 1 (CLN1), also known as infantile neuronal ceroid lipofuscinosis (INCL), is a rare (1 in 100,000 births), but one of the most lethal, inherited neurodegenerative lysosomal storage disorders caused by mutations in the PPT1 gene resulting in PPT1 deficiency.