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 years) 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 survey 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.