Progressive myoclonic epilepsies

The causal disease Progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) is an autosomal recessive neurodegenerative disorder that has the highest incidence among the progressive myoclonus epilepsies worldwide (Berkovic et al. 1986; Marseille Consensus Group 1990). It is characterized by stimulussensitive myoclonus, and tonic-clonic epileptic seizures. As EPM1 progresses, patients develop additional neurological symptoms including ataxia, dysarthria, intentional tremor, and decreased coordination, together reflecting widespread neuronal degeneration in the brain (Koskiniemi et al. 1974a, Norio and Koskiniemi 1979). Some patients become wheelchairbound. Patients may experience emotional lability, depression, and a mild intellectual decline over time, but overall their cognitive functions are less impaired than their motor functions (Koskiniemi et al. 1974a; Lehesjoki and Kalviainen 2007; Kalviainen et al. 2008). Loss-of-function mutations in the gene encoding CYSTATIN B (CSTB) are the primary genetic cause of EPM1 (Lalioti et al. 1997; Pennacchio et al. 1998; Joensuu et al, 2008). Previously EPMl has been known by the following names: Baltic myoclonus, Baltic myoclonic epilepsy, and Mediterranean myoclonus. With advances in genetic testing, these disorders are now collectively classified as EPMl (Kalviainen et al 2008).