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.

Smith-Magenis syndrome (SMS) is a distinct and clinically recognizable multiple congenital anomaly (MCA) and mental retardation syndrome caused by an interstitial deletion of chromosome 17 p11.2. The phenotype of SMS has been well described and includes: a characteristic pattern of physical features; a hoarse, deep voice; speech delay with or without associated hearing loss; signs of peripheral neuropathy; variable levels of mental retardation; and neurobehavioral problems. Although self-injury and sleep disturbance are major problems in SMS, studies are limited on the behavioral phenotype of SMS. This report reviews the current state of knowledge about SMS and presents new data based on syndrome-specific observations by the authors' longitudinal experience working with SMS, specifically related to the behavioral aspects of SMS. This information should have relevance for parents, clinicians, geneticists, and educators involved in the care of individuals with SMS.

The Autism Behavior Checklist (ABC), an assessment instrument for autistic individuals, was evaluated in a group of 157 subjects, 94 clinically autistic and 63 nonautistic. The two groups differed significantly in ratings of pathology. Both false positive and false negative diagnostic classifications were made when the results of the checklist were compared with clinical diagnosis. Effects of developmental level and age were observed. The ABC appears to have merit as a screening instrument, though results of the checklist alone cannot be taken as establishing a diagnosis of autism. Important issues of reliability and validity remain to be addressed.