Case ReportsThe Importance of Thiopurine S-Methyltransferase Gene Analysis Before Azathioprine TherapyGürbüz, Gürkan MD; Edizer, Selvinaz MD; Yılmaz, Ünsal MD; Ünalp, Aycan MDAuthor Information Pediatric Neurology, Dr. Behcet UZ Children's Hospital, İzmir, Turkey. Address correspondence and reprint requests to Gürkan Gürbüz, MD, Pediatric Neurology, Dr. Behcet UZ Children's Hospital, İzmir, Turkey; E-mail: email@example.com Conflicts of Interest and Source of Funding: The authors have no conflicts of interest to declare. Clinical Neuropharmacology: 7/8 2020 - Volume 43 - Issue 4 - p 112-113 doi: 10.1097/WNF.0000000000000397 Buy Metrics Abstract Neuromyelitis optica is an inflammatory central nervous system syndrome associated with serum aquaporin-4 IgG antibody. Optic nerve and spinal cord involvement is typical. We report a 9-year-old girl with a diagnosis of neuromyelitis optica, who developed azathioprine-induced pancytopenia that was subsequently found to be caused by thiopurine-methyltransferase mutation. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.