CSTB and Mental deterioration: Progressive myoclonus epilepsy EPM1 (Unverricht-Lundborg disease; OMIM 254800), caused by biallelic partial loss-of-function mutations in the cystatin B (CSTB) gene (Pennacchio et al., 1996; Joensuu et al., 2008), is a neurodegenerative disorder manifesting with minor or no cognitive decline (Koskiniemi et al., 1974; Kälviäinen et al., 2008).