Geniospasm

Geniospasm is movement disorder of the mentalis muscle.

Geniospasm
Other names	Hereditary geniospasm
Mentalis muscle
Specialty	Neurology

It is a benign genetic disorder linked to chromosome 9q13-q21^[1] 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 8 Hz 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.^{[citation needed]}

The movements are always present but extreme episodes may be precipitated by stress, concentration or emotion and commence in early childhood.^{[citation needed]}

The condition is extremely rare and in a study in 1999 only 23 families in the world were known to be affected,^{[citation needed]} although it may be under-reported. Inheritance is aggressively autosomal dominant. In at least two studies the condition appeared spontaneously in the families.^{[citation needed]}

The condition responds very well to regular botulinum toxin injections into the mentalis muscle^[2] which paralyse the muscle but cause no impairment of facial expression or speech.