Myoclonus in familial restless legs syndrome.

Eighteen members of a family were affected over a span of five generations with the restless legs syndrome, transmitted as an autosomal dominant trait. Ten patients had myoclonus. The propositus, a 57-year-old man, suffered from repeated, intense, asymmetric flexion jerks of the lower extremities, alternating with fidgeting and friction movements of the legs; all occurred at night prior to sleep and severely interfering with it. The patient's movements ceased with the onset of stage 1 sleep, while in his brother, the motor activity persisted in stages 1 and 2 of sleep.