P300 in first degree relatives of schizophrenics.

It has been reported that the amplitude of P300 is low in schizophrenic patients and high risk children. We recorded P300 components of the event-related potentials in first degree relatives of schizophrenic propositi who were considered to be over the age limit of the risk period for manifestation of schizophrenia and compared them with those of schizophrenic patients and controls. Both the first degree relatives and the schizophrenic patients showed lower P300 amplitude than the controls. There was no significant difference between the first degree relatives and schizophrenic patients in the P300 amplitude. These results would indicate that a low P300 amplitude is a trait marker for schizophrenia.