Methylphenidate in KBG Syndrome: N-of-1 Series

KBG syndrome (KBGS) is a neurodevelopmental disorder (NDD) characterized by developmental delay and/or intellectual disability, typical facial features, skeletal and congenital anomalies. Behavioural issues are a frequent feature, reported in 50-94% of persons with KBGS.The behavioural problems are diverse, and include attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), obsessive-compulsive disorder, anxiety, and difficulties in social situations. Van Dongen et al. systematically investigated the behavioural and cognitive phenotype of KBGS patients. This study showed a high level of distractibility, impulsivity and restless behaviour in KBGS patients. As a tertiary reference centre for KBGS in the Netherlands, the investigators notice there is an unmet need for evidence-based interventions for the behavioral problems related to KBGS. A previous survey amongst KBGS caretakers confirmed that (features of) attention-deficit/hyperactivity disorder (ADHD) are the most frequently reported behavioural problems in children with KBGS. Furthermore, the study results indicate that methylphenidate (MPH) has a good effect on ADHD-related symptoms in KBGS, as this is reported by most parents. The promising results from this first exploration on MPH in KBGS indicate that it seems even more effective than in the general population of children with ADHD. However, evidence-based data on optimal dosing and adverse events are lacking. Remarkably, only 2/12 KBGS patients who were treated with stimulants such as MPH had an official ADHD diagnosis. This indicates that patients with ADHD-related symptoms fitting with a probability diagnosis of ADHD, but who do not necessarily fit all the Diagnostic and statistical manual 5 (DSM-5) criteria for ADHD, may also benefit from drug treatment. The investigators will examine the effectiveness of MPH in children and adolescents with KBGS and (a probability diagnosis of) ADHD, using an N-of-1 series (aggregated N-of-1) trial design.