Startle disease (hyperekplexia): a hereditary disorder with abnormal startle, falling spells, and attacks of spontaneous clonus

STARTLE is a basic alerting reaction common to all mammals. A rapid reflex not amenable to voluntary control, startle was studied extensively by Strauss in 1929,1 and is the subject of a 1939 monograph by Landis and Hunt2 and of a more recent study by Gogan.3 In the human adult, except for minor interpersonal variations, a stereotyped motor pattern is seen consisting of eye blinking; facial grimacing; flexion of the head; elevation of the shoulders; and flexion of the elbows, trunk and knees. With repeated stimulation, the intensity of the surprise reaction decreases, but it never completely disappears. Tension, fatigue and heightened expectation of the stimulus enhance it. The intensity is greater in infancy, when the startle reflex appears at the same time as the Moro reflex (an extensor response to sudden stimuli). However, startle becomes more noticeable in time, while the Moro reflex disappears.4 This reflex, so basic to man, can be present in a pathologically exaggerated form which is always embarrassing, sometimes interfering with normal activities; occasionally, it may even be dangerous. The pathophysiology of startle was recently reviewed by Wilkins et al.5 Abnormal, excessive startle is a feature of three distinct conditions (Table I): startle disease (hyperekplexia), jumping (the "jumping Frenchmen of Maine"), and startle epilepsy. The first of these disorders, hyperekplexia, is described here.