Geniospasm is

movement disorder Movement disorder refers to any clinical syndrome with either an excess of movement or a paucity of voluntary and involuntary movements, unrelated to weakness or spasticity. Movement disorders are synonymous with basal ganglia or extrapyramidal d ...

of the

mentalis The mentalis muscle is a paired central muscle of the lower lip, situated at the tip of the chin. It originates from the mentum of the mandible, and inserts into the soft tissue of the chin. It is sometimes referred to as the "pouting muscle" due ...

muscle. It is a benign genetic disorder linked to chromosome 9q13-q21 where there are episodic involuntary up and down movements of the

chin The chin is the forward pointed part of the anterior mandible ( mental region) below the lower lip. A fully developed human skull has a chin of between 0.7 cm and 1.1 cm. Evolution The presence of a well-developed chin is considered to be one ...

and

lower lip The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

. 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 The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste bu ...

and buccal floor muscles may also be affected but to a much lesser degree. The movements are always present but extreme episodes may be precipitated by stress, concentration or emotion and commence in early childhood. The condition is extremely rare and in a study in 1999 only 23 families in the world were known to be affected, although it may be under-reported. Inheritance is aggressively autosomal dominant. In at least two studies the condition appeared spontaneously in the families. The condition responds very well to regular

botulinum toxin Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromu ...

injections into the mentalis muscle which paralyse the muscle but cause no impairment of facial expression or speech.

References

External links

{{Medical resources , ICD10 = G25.3 , ICD9 = , ICDO = , OMIM = 190100 , DiseasesDB = , MedlinePlus = , eMedicineSubj = , eMedicineTopic = , MeSH = C537682 , GeneReviewsNBK = , GeneReviewsName = , Orphanet = 53372 Neurological disorders