Williams syndrome (WS) is associated with cognitive deficits, special behavioral phenotype, and high rates of psychiatric disorders. The aims of the present study were: (1) To compare the rates of psychiatric disorders and repetitive behaviors in children with WS to children with idiopathic developmental disability (DDs); (2) To longitudinally assess the change in psychiatric disorders during adolescence in WS; (3) To assess retrospectively the effectiveness and safety of methylphenidate (MPH) treatment in WS children with ADHD. The study consisted of a cohort of 38 children and adolescents (age 13.1 ± 5.2 years) with WS and a sample of age-matched DDs (age 15.0 ± 3.1 years). A current follow-up evaluation was conducted after 5.6 ± 1.6 years for 25 subjects (65.8%) of the WS cohort. The rate of most psychiatric disorders was found similar in children with WS and DD controls. Specific phobia, especially from noises, obsessive-compulsive symptoms (e.g., aggressive obsessions and repetitive questions), and stereotypic behaviors (e.g., glancing), were more common in WS than DDs. In a longitudinal follow-up of the WS children, we found a decrease in the rate of anxiety disorders. In addition, a clinically significant improvement was reported in 72.2% of WS children with ADHD following MPH treatment. Sadness/unhappiness was the most common side effect associated with MPH treatment in WS, occurring in 2/3 of treated individuals. The present study further elucidates the neuropsychiatric phenotype of WS. Our results also suggest that MPH treatment for ADHD in WS warrants future prospective controlled trials.
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