Clinical and molecular genetic data on a family from the United States in which four of five sibs were affected with progressive myoclonus epilepsy of Unverricht-Lundborg type are reported from the University of Helsinki, Finland; National Cancer Institute, Bethesda, MD; and the VA Hospital, University of Florida, Gainesville, FL. Onset was between 9 and 11 years with grand mal seizures. Progressive stimulus-sensitive myoclonus developed at 11 to 13 years of age. Generalized spike-wave and polyspike-wave paroxysms and photo-sensitivity were characteristic EEG findings. The gene (EPM1) has been mapped to chromosome 21 in Finland, and the gene in this non-Finnish American family was also linked to the EPM1 region. Crossover events refined the gene localization between loci CBS and D21S112, leading to greater accuracy of genetic prediction based on linkage analysis. [1]

COMMENT. Causes of progressive myoclonus epilepsy include Unverricht-Lundborg disease (ULD), Lafora’s disease, MERRF, Kufs’ neuronal ceroid lipofuscinosis, and sialidoses. ULD is relatively common in Finland. Cochius JI et al, at the Montreal General Hospital, have performed linkage analysis in 8 families, including 4 of neither Baltic nor Mediterranean origin. They report that ULD diagnosed in areas remote from the Baltic maps to the same locus on chromosome 21 as the Finnish form, and suggest that all ULD, regardless of geographic origin, represent mutations of the same gene [2]. Lafora’s disease, characterized by intraneuronal inclusions, is a form of myoclonus epilepsy not linked to EPM1 and chromosome 21. The recent advances in molecular genetics of neurological disease are reviewed in two current journals: Rosenberg RN et al. [3, 4]