Progressive myoclonic epilepsy type 1 (EPM1), also called Unverricht-Lundborg disease, is an autosomal recessive disorder caused by mutations in the cystatin B (CSTB) gene, which acts as a cysteine protease inhibitor (Pennacchio et al., 1996; Lalioti et al., 1997a, b). Here, CTSB is linked to Unverricht-Lundborg disease.