Geniospasm is movement disorder of the mentalis muscle. It is a benign but socially excluding genetic disorder linked to chromosome 9q13-q21 where there are episodic involuntary up and down movements of the chin and lower lip. The movements consist of rapid fluttering or trembling at about 8Hz superimposed onto a once per three seconds movement of higher amplitude and occur symmetrically in the V shaped muscle. The tongue and buccal floor muscles may also be affected but to a much lesser degree.
* Quivering chin * Quivering lower lip