[Hereditary quivering of the chin in a West Spanish family].

An unusual hereditary tremor which affects only the m. mentalis is reported. In four generations of a West Spanish family 20 members exhibited the symptom. It presents a quick rhythmic contractions of the m. mentalis with a frequency of 6-11/s. The amplitude varies greatly. The trembling of the chin appears at intervals from birth and may last seconds or minutes with shorter or longer asymptomatic periods. Stress or excitement can cause or intensify the symptoms. The quivering of the chin found in this West Spanish family does not differ from that described in 11 other families reported in the literature. They are all clinically identical with each other, and in the 12 families the symptom follows an autosomal dominant mode of inheritance. The penetrance is slightly reduced, and both sexes are equally affected. It is not serious, but for the patients it is a rather tedious anomaly which is hardly ever reported to a physician.