Neurophysiological investigations in GM1 and GM2 gangliosidoses.

Neurophysiological studies (EEG, ERG, VEP and BAEP) have been carried out on a total of fifty-four patients (fourty-five GM2 and nine GM1 gangliosidosis) at various stages of the disease process. In infantile GM2 gangliosidosis, the EEG was midly abnormal from an early age but by the age of one year there was a rapid and progressive deterioration. EEG changes in late onset GM2 gangliosidosis were very variable and unrelated to age or enzyme defect. In both Type 1 and Type 2 GM1 gangliosidosis there was a progressive deterioration of the EEG. Paroxysmal features were not prominent in any of the gangliosidoses, despite the occurrence of seizures. The ERG remained normal in both GM2 and GM1 patients. In the infantile GM2 patients there was progressive loss of the VEP between nine and fifteen months of age but the timing of VEP changes were more variable in all the other groups. Evidence of brainstem dysfunction was found in one of the two TSD patients tested. The combined neurophysiological features appear to be characteristic for each group of gangliosidosis and differ from other neurometabolic disorders of childhood.