Periodic limb movement in sleep in children with Williams syndrome

Objective: Williams syndrome (WS) is associated with neurobehavioral abnormalities that include irritability and attention-deficit/hyperactivity disorder. Parents often report children having difficulties initiating and maintaining sleep because of restlessness and arousals. Therefore we evaluated a group of children with WS for the presence of a movement arousal sleep disorder. Methods: Twenty-eight families of children with WS participated in a telephone survey aimed to screen for a movement arousal disorder. Of the 16 children identified as having such a disorder, 7 (mean age, 3.9 +/- 2.2 Sears) underwent polysomnography. Their studies were compared with those of 10 matched control subjects (mean age, 5.3 +/- 2.0 years). Results: The 7 subjects with WS who were screened by the sun ey had sleep latency, total sleep time, arousals, and awakenings that were similar to those of control subjects. However, they presented with a disorder of periodic limb movement in sleep (PLMS). The PLMS index in the subjects with WS was 14.9 +/- 6.2 versus 2.8 +/- 1.9 in control subjects (P <.0001). In addition, arousal and awakening in subjects with WS were strongly associated with PLMS. Moreover, children with WS spend more time awake during sleep periods than control subjects (10.0% +/- 7.0% vs 4.4% +/- 4.7%; P <.05). Five children were treated with clonazepam, and in 4 a significant clinical response was noted. Conclusion: We report an association between WS and PLMS. Clonazepam may reduce the clinical symptoms of PLMS in some of these children.