Chromosome 22q11 deletions and severe learning disability

In a previous study (Murphy et al, 1998) we identified 74 patients thought to be at risk of velo-cardio-facial syndrome (VCFS) from 265 hospitalised individuals with learning disability. We screened these 74 people and found two cases of VCFS, giving a minimum prevalence of 0.7% in the entire sample. Recently, we found a further individual with VCFS among the 191 individuals who were not selected for screening. This gives a revised minimum prevalence estimate of 1.1%.

The patient, a 50-year-old Caucasian female with severe learning disabilities, had no reported complications arising during gestation, delivery or early childhood. Developmental milestones were globally delayed. She presented to the psychiatric services as a teenager with a 12-month history of becoming withdrawn and subdued, having lost some previously learned skills and displaying outbursts of bizarre behaviour and aggression. She was subsequently admitted on several occasions and was definitively admitted as a long-term patient within 2 years of initial presentation, owing to her enduring challenging behaviour. At this time, her mental age was assessed to be between 2 and 4 years and she had not developed any effective speech or signing. She remained in hospital for over 30 years, then was discharged to a staffed house in the community. While in hospital she remained largely quiet, timid and withdrawn. However, there were episodes of prolonged challenging behaviour, during which time she became suspicious, would scream, cry and make unintelligible noises, often accompanied by physical aggression. These episodes were treated with a variety of behavioural modification strategies, augmented with various antipsychotic preparations with partial success. No formal diagnosis of psychotic illness was made and she was therefore not selected for chromosome 22q11 deletion studies as she did not meet screening criteria (Murphy et al, 1998).

In 1999 she was readmitted to the local assessment and treatment unit because of aggression, agitation, deterioration in her skills and bizarre behaviour including ambitendence, vocalising and gesturing as if responding to abnormal perceptions. It was felt that these symptoms were suggestive of a psychotic disorder and she was successfully treated with an atypical antipsychotic. A provisional diagnosis of schizophrenia was made, although one cannot be categorical in individuals lacking effective communication skills (Royal College of Psychiatrists, 2001). Fluorescence in situ hybridisation (FISH) analysis confirmed a deletion or chromosome 22q11.

In our 1998 study, we concluded that chromosome 22q11 deletions appear to be aetiologically significant in a proportion of individuals with idiopathic learning disability, especially in those with mild learning disability and psychosis. The importance of the patient described above is that she has severe rather than mild learning disability and that, despite presenting with seriously challenging behaviour at the time of the study, she was not diagnosed as having a formal psychotic illness.

Although individuals with VCFS are characterised predominantly by borderline or mild learning disability, it is important for clinicians to be aware that occasionally such individuals may present with more severe learning disabilities, as in this case. We suggest that any individual with moderate or severe learning disabilities with a history of bizarre or uncharacteristic challenging behaviour, even in the absence of a formal diagnosis of psychosis, should be referred for chromosome 22q11 deletion studies.