Northern epilepsy, a new member of the NCL family
Northern epilepsy, or progressive epilepsy with mental retardation (EPMR), is an autosomal recessive disorder characterized by normal early development, onset of generalized tonic-clonic seizures between the ages of 5 and 10 years, and subsequent progressive mental retardation. The seizures increase in frequency until puberty after which the epileptic activity starts to decline. Mental retardation begins 2–5 years after the onset of seizures and continues through adulthood. Neuropathological findings have shown that EPMR is a new member (CLN8) of the neuronal ceroid lipofuscinosis (NCL) groups of neurodegenerative disorders. The CLN8 gene was identified recently. It encodes a 286 amino acid putative transmembrane protein with no homology to previously known proteins. Subsequently, the homologous mouse gene (Cln8) was sequenced and localized to the region of the mouse genome linked to motor neuron degeneration, mouse mnd. Mnd is a naturally occurring mouse mutant with intracellular autofluorescent inclusions similar to those seen in human CLN8. A mutation in mnd mouse DNA was identified, indicating that mnd is a murine model for CLN8.