GENIOSPASM - HEREDITARY CHIN TREMBLING

Geniospasm is a hereditary disorder characterized by episodic, usually stress-induced involuntary trembling of the chin. Nineteen families f rom Europe and the U.S.A. suffering from this disorder have been descr ibed since 1894. We present three cases from two newly detected famili es. There was no evidence of any other nervous system abnormality, alt hough abnormal EEG, sleep disorders, and involvement of other facial m uscles have been described in rare cases. Geniospasm is transmitted as an autosomal-dominant trait with high penetrance. It must be differen tiated from facial myokymia, palatal tremor, and essential tremor affe cting facial muscles. Neurophysiological and molecular mechanisms of t his peculiar disorder are unknown.