Certain homozygous or compound heterozygous CLN8 mutations cause two distinct variants of neuronal ceroid lipofuscinosis-8 (CLN8; OMIM#600143): Northern epilepsy variant (OMIM#610003), also known as progressive epilepsy with mental retardation (EPMR), and a more severe form of variant late-infantile neuronal ceroid lipofuscinosis (vLINC). Here, CLN8 is linked to CLN8 disease.