“N of 1” Trials of Methylphenidate in Two Children with Williams Syndrome and Attention Deficit Hyperactivity Disorder

Poor attention and motor restlessness are common in Williams syndrome (WS) children, and attention deficit hyperactivity disorder (ADHD) is at least as prevalent in WS as in other mentally handicapped groups. We determined the effectiveness of methylphenidate in two children with WS and ADHD. Each child underwent a double-blind dose-determining assessment to select the optimum dose for “N of 1” trials, which consisted of single subject, placebo-controlled randomized controlled trials with multiple crossovers. A regimen of 5 mg in the morning and 2.5 mg at noon was determined by consensus for both trials. Response to MPH was assessed using parent and teacher Conners ratings, and analyzed separately for each child, using mixed model ANOVA. No significant differences in behavioral ratings between medication and placebo weeks were found during the “N of 1 trials.” We conclude that methylphenidate was not superior to placebo in decreasing ADHD symptoms in these two children with Williams syndrome.