A case with myoclonic jerks, grand mal convulsions and progressive mental retardation is reported. The patient died after 4 years and 10 months of disease, and a sister began with similar simptomatology at this time. By histopathological study there were found intracitoplasmatic bodies in the cerebral cortex, basal ganglia, cerebelum and myocardium. Some considerations are made about clinical, polygraphic histological and etiopathogenic aspects.