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Two unrelated patients with the cherry red spot--myoclonus syndrome, a rare chronic neuronal storage disorder that begins in childhood with progressive myoclonus, cherry red spots at the macula, and easily controlled seizures, but no dementia, have been investigated electrophysiologically in order to characterize the myoclonic and electroencephalographic features of this syndrome. Phenomenologically, the disease most closely resembles the Ramsay Hunt syndrome, although certain unique features are noted and the patients are not photosensitive. Pathologically and clinically, the disease is related to mucolipidosis type I and atypical cases of GM1 gangliosidosis, and the EEGs obtained from our patients are identical to those seen in mucolipidosis type I. Because of the unusual clinical picture presented in this disease, there should be no difficulty in differentiating it from other more malignant storage disorders and progressive myoclonus epilepsies of childhood. Electrophysiological findings suggest that the myoclonic jerks do not originate cortically, but the specific subcortical generators have not been identified.