Nonketotic hyperglycinemia: electroencephalographic and evoked potential abnormalities

Five patients with nonketotic hyperglycinemia had serial EEGs and evoked-response studies. EEGs were grossly abnormal in all patients. In the neonatal period, the "suppression-burst" pattern was observed. The EEG changed to hypsarrhythmia during early or mid-infancy. In the second to fifth years of life, multifocal epileptiform discharges superimposed on diffuse slow background activity constituted the usual abnormality during wakefulness, but more severe disorganization of the EEG occurred in sleep with emergence of hypsarrhythmia. Four patients had abnormal brainstem auditory evoked responses, characterized by prolongation of I-V interval, and two had abnormal flash-induced visual evoked responses.