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Distinctiveness and correlates of maladaptive behaviour in children and adolescents with Smith-Magenis syndrome.

This two-part study examines the distinctiveness and correlates of maladaptive behaviour in 35 children and adolescents with Smith-Magenis syndrome, a developmental disorder caused by an interstitial deletion of chromosome 17 (p11.2). Study I compares Child Behavior Checklist scores in 35 children with Smith-Magenis syndrome to age- and gender-matched subjects with Prader-Willi syndrome and mixed intellectual disability. Subjects with Smith-Magenis syndrome had significantly higher levels of maladaptive behaviour than the other groups. Although some problems were shared across groups, 12 behaviours differentiated the three groups with 100% accuracy. Study 2 assessed the frequency and correlates of self-injurious and stereotypical behaviours, including unusual features such as nail-yanking, inserting objects into bodily orifices, self-hugging and a 'lick-and flip' behaviour. Nail-yanking and bodily insertions were less common than other types of self-injury, and self-hugs and the 'lick-and flip' stereotypies were seen in about half the sample. Although age and degree of delay were correlated with problem behaviours, sleep disturbance emerged as the strongest predictor of maladaptive behaviour. The implications are discussed for clinical diagnostic ambiguities between the Smith-Magenis and Prader-Willi syndromes, and for intervention.