Mental health comorbidity is higher in those with learning disability especially those who are within forensic services than the general population and diagnostic overshadowing is a particular problem. Hence, all behavioural or mental health related presentations are often attributed to the learning disability and vice versa without an adequate investigation of the causes of learning disability. This is a case report of a young male with mild LD with longstanding mental health and behavioural problem who was described as having a personality disorder in the community. Systematic diagnostic evaluation showed the presence of 22q11.2 Duplication Syndrome. While adding to the sparse literature on the behavioural and physical phenotype of the syndrome, it also allowed his mental health presentation to be re-formulated. This changed his treatment plan and outcome.

28-year-old, single, Caucasian male with delayed developmental milestones who was referred to Children Mental Health Services for behavioural difficulties and ADHD-like features. In early adulthood, behavioural problems continued with aggression towards others and was under the care of a community mental health team although with lack of diagnostic clarity and poor compliance. Violence towards self and others led to several short hospital admissions, mainly because he tended to discharge himself against medical advice. The predominant diagnostic formulation was one of a young man with mild learning disability + psychosis related to substance misuse + personality disorder. Facing multiple charges of assault, the court, on medical advice, gave him a hospital order to a medium secure unit for people with learning disabilities where he went through a detailed and systematic diagnostic evaluation that revealed several new findings. Based on this, he went through the 10-point-treatment programme.

Clinicians need to be aware of diagnostic overshadowing leading to misattribution and consequently poor treatment. In this case, the sensory impairments associated with 22q11.2 Duplication Syndrome affected his communication. His tunnel vision led him to bump into people in pubs and other public places giving impression of deliberate antisocial behaviour. The atypical autism, learning disability and co-existing mental illness further complicated the picture. Confirmation of the underlying genetic syndrome and its physical and behavioural phenotype led to a different diagnostic and psychological formulation from the earlier one which was based on a personality disorder. It also allowed more targeted treatment strategies and the patient could be discharged back to the community from a secure hospital setting.

22q11.2 Duplication Syndrome is a rare genetic syndrome that can cause learning disability. Its physical and behavioural phenotypic features described in literature, were all present in this patient. In addition, this case report highlights three previously unreported findings: Cochlear Nerve Atresia, Tubular Vision, the Characteristic groove and skin fold on the back of the scalp and the presence of a schizoaffective mental illness.