• hereditary chin trembling
• autosomal dominant;

Hereditary chin trembling1 is a rare autosomal dominant condition described in the literature as “geniospasm”, “facial spasm”, “Ein streng dominant erbliches kinnmuskelzittern”, “familial trembling of the chin”, “hereditary quivering of the chin”, and “trembling chin”. In 19931 up to 21 affected families had been reported. The male:female ratio was 1.3:1. There were 20 white families (United States and central Europe) and one black family. We present a new white family (figure 1) which gives us the opportunity to discuss the nature of the abnormal involuntary movement.

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Figure 1

Pedigree of family. Affected members in black (↗=proband).

The index case (IV-13) was a 35 year old sales representative who was examined because of abnormal involuntary movement of the chin. This had been present since birth, constantly during childhood, and then episodically, lasting a few minutes. It appeared electively in stressful situations such as playing videogames, pinball, or in working hours when meeting customers. He had been free of symptoms for two years but the abnormal involuntary movement reappeared a few months before examination after buying a computer for work and pleasure. It was described as a tremulous movement of the chin but he said that once he had noted that the abnormal involuntary movement had spread to the upper lip. During some periods with severe stress, the abnormal involuntary movement was so great that it was present during sleep and sometimes woke him up

He was unable to initiate or suppress it. On examination a quick, up and down, tremulous bilateral movement was sometimes spontaneously seen at the tip of his chin for a few minutes. Whether this abnormal involuntary movement was present or not, there was neither postural hand tremor, head tremor, voice tremor, or palatal myoclonus, and a general neurological examination was negative. He wanted to be treated because he found the abnormal involuntary movement socially disabling in his professional activities even though he knew that it was benign, many members of his family having had the same problem.

His brother (IV-12) had had the same abnormal involuntary movement since birth. It was less severe and without social or professional consequences. Two female first cousins (IV-8 and IV-9) presented the abnormal involuntary movement with the same characteristics. A 30 year old male first cousin (IV-1) and three female first cousins (IV-6: 34 years old; IV-8: 43 years old ; IV-9: 27 years old) had had very slight abnormal involuntary movement from birth until they were a few months old. An 11 year old boy (V-20) was socially disabled because under some circumstances the abnormal involuntary movement could be so intense that speaking was impaired. A 4 year old girl (V-22) was the daughter of the proband. The trembling chin had been present very early in life; it had been seen by her father a few minutes after birth, in the delivery room. According to her father the abnormal involuntary movement could be seen when she was sleeping. Three young boys (V-6, V-7, and V-8) had the same abnormal involuntary movement but very rarely. The mother of the proband (III-6) was 62 years old. She also had had the chin tremor when an infant but it progressively disappeared with time. It had not been clinically seen for many years but she said that she felt shiverings when stressed. A 65 year old woman (III-5) had had chin tremor when a child but it was rapidly only seen in stressful situations and had not been noticed for 10 years. Two men (III-3 and llI-4) were said never to have had chin tremor but they both had a child with this abnormal involuntary movement. No patient’s symptoms were improved by alcohol intake. No member of this family, with or without an abnormal involuntary movement of the chin, had other abnormal involuntary movements.

Electrophysiological studies were carried out on the proband. The EMG activity was obtained from mentalis muscle with two surface electrodes placed 2 cm apart, filtered (20 Hz-2 kHz), and amplified. An accelerometer was attached to the chin. The signal was fed to the EMG device and to a PC to obtain spectral analysis. Several 10 second recordings were made with a sampling rate of 100 Hz. When appropriate, different activation manoeuvres were used to enhance the movement disorder, such as playing with his daughter. Figure 2 shows the results.

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Figure 2

Surface EMG activity of mentalis muscle (traces 2, 4, 6, 8) and “tremorogram” (traces 1, 3, 5, 7) obtained from an accelerometer placed on the chin. During playing activities, there are brief bursts of EMG, pseudorhythmic or irregular, without sinusoidal oscillations.

The peak frequency of chin “tremor” varied widely between 5.7 and 10.3 Hz. Intermittently, brief (10-25 ms duration) bursts of activity were seen, especially during stressful and playing activities. Sometimes the bursts discharged in a rhythmic fashion and had the appearance of a clinical tremor; but most often the frequency of discharge was irregular.

Simultaneous recording of video, EEG, and EMG of the mentalis muscle was made with digital equipment (Deltamed, Paris). EEG activity was obtained from 19 surface electrodes placed on the scalp according to the international 10-20 system and low pass filtered at 256 Hz with a time constant of one second. The EEG signals were back averaged off line with respect to the EMG bursts.

Standard EEG showed no anomaly. Back averaging the EEG before the jerks failed to disclose any potential.

Sensory evoked potentials were measured using an eight channel Nicolet Pathfinder II, with the subject lying supine in a quiet dark room. Median nerves were stimulated at the wrist with surface electrodes, using 0.1 ms constant current square pulses with an intensity of 1.2 above motor threshold at a rate of 3.3 Hz. Recordings were obtained from Erb’s point, cervical (C6), C′3, C′4, F′3, and F′4, with an earlobe reference contralateral to the stimulation, and also from the abductor pollicis brevis muscle ipsilateral to the stimulation. Trigeminal evoked potentials were obtained by stimulating the skin of the lips with surface electrodes, using 0.1 ms constant current square pulses with an intensity of three times subjective threshold, at 2.7 Hz. Cortical responses were recorded from an electrode placed contralateral to the stimulation side on the midpoint of a line joining the external auditory meatus and a point I cm posterior to Cz, with an Fz and earlobe reference. For each nerve, two series of 500 stimulations were averaged.

All cortical responses were of normal latency and amplitude. There was no C-reflex, even after muscular activation (for upper limbs).