Familial nocturnal cramping

A familial syndrome of painful nocturnal cramping and jerking in members of three generations is described. All-night polysomnograms demonstrated both myoclonic jerks and sustained muscular activity in three family members, a 4-year-old girl, who presented with frequent episodes of painful awakenings; her 7-year-old brother, who had similar but less severe symptoms; and the 28-year-old mother, who had suffered nocturnal cramping and awakenings for much of her life. To the authors' knowledge, this is the first description of a familial disorder characterized by exclusively nocturnal intermittent cramping and myoclonus of brainstem or spinal origin.