Neuronal ceroid lipofuscinosis type 1 (CLN1) disease, also known as infantile neuronal ceroid lipofuscinosis, is a rare and fatal neurodegenerative condition. CLN1 disease is caused by a deficiency in the enzyme palmitoyl-protein thioesterase 1 (PPT1) due to biallelic loss-of-function mutations in the gene encoding the lysosomal enzyme, leading to widespread neurological dysfunction and premature death.