Further evidence for high rates of schizophrenia in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11.2DS) is associated with high rates of psychotic disorder, particularly schizophrenia. The deletion is considered to be a biological model for understanding this debilitating psychiatric disorder. It is unclear whether the psychotic manifestations in 22q11.2DS are similar to those in schizophrenia patients without the deletion. Catechol-O-methyltransferase (COMT), a positional candidate gene for schizophrenia, resides within the 22q11.2 region. It remains unknown whether hemizygosity for this gene is associated with risk of psychotic disorder. This study includes 83 adults with 22q11.2DS, 90 non-deleted individuals with schizophrenia, and 316 normal controls. Psychopathology was assessed using the Schedules for Clinical Assessment in Neuropsychiatry, the Schedules for the Assessment of Positive and Negative Symptoms and the Global Assessment Scale. Schizotypy was assessed with the Kings Schizotypy Questionnaire and Oxford Liverpool Inventory of Feelings and Emotions. IQ estimates were also obtained. Adults with 22q11.2DS were genotyped for a number of COMT polymorphisms as well as the Ashkenazi risk haplotype. This study confirms high rates of psychotic disorder (29%) in individuals with 22q11.2DS of which the majority had schizophrenia (22%). There does not appear to be a differential expression of schizophrenic symptom clusters in 22q11.2DS in relation to sporadic schizophrenia, though schizophrenia in 22q11.2DS seems to be less severe in terms of global assessment scores. Psychosis proneness seems to be of genetic origin in 22q11.2DS as individuals with 22q11.2DS without schizophrenia had higher schizotypy scores than normal controls. Finally, COMT was not associated with schizophrenia status or schizotypy.