Variable expressivity in familial restless legs syndrome.

A 62-year-old man with a 20-year history of excessive daytime somnolence and kicking during sleep was an obligate carrier of the restless legs syndrome gene because his paternal grandfather, father, and all three of his children had symptoms of restless legs syndrome. The patient himself, however, denied motor restlessness after a careful and exhaustive medical history and he was originally believed to have periodic movements in sleep without restless legs. Close clinical observation did reveal nighttime motor restlessness, although the patient continued to deny its importance. Polysomnography showed frequent periodic movements in sleep. We conclude that there can be variable expressivity of the clinical features in familial restless legs syndrome and that there are probably some relatively nonrestless patients with prominent periodic movements in sleep who are carriers of the restless legs syndrome gene. Some sleep-disordered patients who are believed to have only periodic movements in sleep may have a forme fruste of autosomal dominant restless legs syndrome. If one does not examine these patients carefully at night and take an adequate family history, one may miss the diagnosis of restless legs syndrome.