Brief ReportPsychosis and autism without functional regression in a patient with Kleefstra syndromeColijn, Mark A.a,b; Lakusta, Cherelyn M.a; Marcadier, Julien L.c Author Information aDepartment of Psychiatry, The University of Calgary bHotchkiss Brain Institute, The University of Calgary cDepartment of Genetics, Alberta Children’s Hospital, Calgary, Alberta, Canada Received 16 July 2022 Accepted 11 October 2022. Correspondence to Mark A. Colijn, MD, MSc, FRCPC, Department of Psychiatry, University of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4, Canada, Tel: +587 228 5862; e-mail: [email protected] Psychiatric Genetics 33(1):p 34-36, February 2023. | DOI: 10.1097/YPG.0000000000000330 Buy Metrics Abstract Kleefstra syndrome is a rare genetic disorder caused by haploinsufficiency of the euchromatic histone lysine methyltransferase 1 (EHMT1) gene. It is characterized by a variety of dysmorphic features, comorbid medical issues, and developmental delays/intellectual disability. Neuropsychiatric symptoms may also occur, including autistic features and psychosis, and are often accompanied by functional regression. However, the phenomenology of psychotic symptoms in this syndrome has not been well described in the literature. As such, in this brief report, we review the literature with respect to the occurrence of psychosis in Kleefstra syndrome and describe the symptom profile of a 35-year-old affected male with an intellectual disability, autism spectrum disorder, and schizophrenia (in association with manic features). This is the first report of psychotic symptoms fully remitting in response to zuclopenthixol therapy in an individual with Kleefstra syndrome. This case is also unique as it demonstrates that functional regression does not necessarily coincide with the development of schizophrenia-like presentations in affected individuals. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.