Abstract
Deletion in chromosome 16 at location 11p.2 has been associated with multiple neurodevelopmental disorders including intellectual disability; autism spectrum disorder (ASD) and impaired social communication and interaction; behavioural dysfunctions including oppositional defiant disorder (ODD) and other disruptive behavioural disorders such as aggression, irritability, and noncompliance; and impaired/ delayed development of speech and language.
To the best of our knowledge, there is no known pharmacological approach to address early stage of the neurobiological pathogenesis of this neurodevelopmental disorder.
Methods: Two-year-old boy, with established diagnosis of 16p11.2 microdeletion syndrome, has been referred to Child and Adolescent Mental Health community service, the Northern of the Netherlands due to intolerable disruptive behaviour. Besides, this toddler demonstrated absence of expressive language, social impairment, headbanging and other motor stereotypies. Treatment with risperidone was started and the effect of treatment has been evaluated during a follow up period of 16 weeks using clinical interview with the parents, inspection of toddler’s behaviour and by using Child Aberrant Behaviour Checklist.
Results: Clinically meaningful improvement has been observed in the 3 main affected neurodevelopmental domains, expressive language, behavioural disorder and social communication could be observed during the follow up period.
Conclusion: Risperidone - induced improvement in the 16p11.2 microdeletion associated neurodevelopmental deficits calls for further investigations to explore the potential therapeutic role of antipsychotics in the early phases of this syndrome and other conditions sharing the same neurobiological pathogenesis including autism spectrum disorder.

Key words: 16p11.2 microdeletion, Risperidone, Language impairment, Behavioural disorder, Social skills