Chapter 67 - Progressive Myoclonus Epilepsies

Abstract

This chapter describes progressive myoclonus epilepsies (PME). The term PME refers to a clinically definable subgroup of rare genetic disorders among the symptomatic generalized epilepsies. The EPM1 gene for PME of Unverricht-Lundborg type was assigned to the long arm of chromosome 21, band q22.3 (21q22.3) by linkage analysis in 12 Finnish families using polymorphic restriction fragment length (RFLP) markers. The localization of the EPM1 gene was precise enough to encourage the search for EPM1 candidate genes. The direct cDNA selection method was used to identify cDNA segments from the 175-kb region. Lafora's disease is an autosomal recessive inherited disease entity among PME. Myoclonus epilepsy associated with ragged-red fibers (MERRF), is emerging as one of the most common causes of PME. The clinical features of MERRF include myoclonus, tonic-clonic seizures, dementia, ataxia, myopathy, neuropathy, mild cardiomyopathy, hearing loss, optic atrophy, and lipomas. Point mutations in other mitochondrial genes encoding transfer RNAs have been described in single MERRF families. The neuronal ceroid-lipofuscinoses and variant late infantile ceroid-lipofuscinosis are also elaborated.