Introduction THE FAMILIAL form of myoclonus epilepsy was first described by Unverricht in 1891.1Subsequent reports have indicated that the myoclonus is merely one of the clinical features of a progressive polioencephalomyelopathy with varied pathologic findings and presumably different etiologies.2A-2DGrand mal attacks, progressive motor deficits, amaurosis, and advancing mental deterioration are prominent features of the disorder. With anticonvulsive drugs the myoclonus and the grand mal attacks may be suppressed. Then the clinical picture is characterized by increasing dementia and motor defects quite similar to other progressive adolescent dementias. The intraneuronal inclusions of Lafora3A,3Bhave been the dramatic neuropathologic finding. This intracellular material has been identified as belonging "to the group of acid mucopolysaccharides."4Similar material has been found in the heart muscle and liver cells of possibly eight cases.4-9Such studies have indicated that Unverricht's syndrome may well be part of some as