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Neurogenetics

"Geniospasm" was coined in 1894 for a hereditary trembling of the chin. 27 families from Europe and the USA with more than 350 affected members have been identified since. The peculiar tremor disorder is transmitted as an autosomal-dominant trait with approximately 80% penetrance and slight male preponderance. Its molecular basis is unknown as is a possible relationship to essential tremor.
Ten patients (7 male, 3 female) from three families were studied in detail. The youngest subject was 4 months old, the oldest 68 years. All showed the typical intermittent, usually stress-induced quivering of the skin overlving the chin. This correlates with 8-30Hz discharges of groups of motor units in the mentalis muscle bilaterally.
From clinical examination, there was no evidence for additional nervous system abnormality, although abnormal EEG, sleep disorders and involvement of other facial muscles have been described in rare cases of this essentially benign condition. In a single patient, local botulinum toxin injections succeeded in temporary abolishment of the symptom.
We have collected DNA from four additional families. Pedigree sizes, however, are yet insufficient for linkage studies.


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Geniospasm

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