TREMBLING CHIN (GENIOSPASM)

Trembling chin is a benign hereditary trait (McKusick catalogue number 19010), first reported from Sicily by Massaro in 1894 under the name of "geniospasm" (in analogy to blepharospasm). It since has been documented in 18 families from Europe and the USA, transmitted as an autosomal-dominant trait with 66% to 100% penetrance. It consists of intermittent spontaneous or stress-induced quivering of the skin overlying the chin bilaterally. We describe clinical and electromyographic findings in five subjects from a newly detected family from upper Bavaria with 13 affected members in 4 generations. Clinically, chin trembling is an isolated finding and correlates with spontaneous motor unit discharges in the mentalis muscle. Pathophysiology, nosology and molecular genetics need to be elucidated.