Familial startle disease (hyperexplexia). Electrophysiologic studies.

Six affected members from a family of 15 patients with familial startle disease (hyperexplexia) underwent extensive electrophysiologic evaluation. The most marked abnormality consisted of prominent C response 60 to 75 ms after median and peroneal nerve stimulation. The somatosensory evoked responses were also relatively high in amplitude. These findings suggest that hyperactive long-loop reflexes may constitute the physiologic basis of startle disease.