Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 21 1 2022 02 06 92 97 Sule Haskologlu Department of Pediatric, Immunology and Allergy and Hematopoietic Stem Cell Transplantation Unit, School of Medicine, Ankara University, Ankara, Turkey Kubra Baskin Department of Pediatric, Immunology and Allergy and Hematopoietic Stem Cell Transplantation Unit, School of Medicine, Ankara University, Ankara, Turkey Caner Aytekin Pediatric Immunology Clinic, Dr. Sami Ulus Obstetrics and Gynecology and Pediatric Health and Diseases, Training and Research Hospital, Ankara, Turkey Candan Islamoglu Department of Pediatric, Immunology and Allergy and Hematopoietic Stem Cell Transplantation Unit, School of Medicine, Ankara University, Ankara, Turkey Serdar Ceylaner Intergen Genetic Diagnostics Center, Ankara, Turkey Figen Dogu Department of Pediatric, Immunology and Allergy and Hematopoietic Stem Cell Transplantation Unit, School of Medicine, Ankara University, Ankara, Turkey Nurdan Tacyildiz Department of Pediatric, Hematology and Oncology, School of Medicine, Ankara University, Ankara, Turkey Emel Unal Department of Pediatric, Hematology and Oncology, School of Medicine, Ankara University, Ankara, Turkey Aydan Ikinciogullari Department of Pediatric, Immunology and Allergy and Hematopoietic Stem Cell Transplantation Unit, School of Medicine, Ankara University, Ankara, Turkey 2021 02 02 2021 07 24 Loss-of-function mutations in magnesium transporter 1 (MAGT1) gene cause X-linked magnesium deficiency with Epstein–Barr virus (EBV) infection and neoplasm (X-MEN), a disease with quite diverse clinical and immunological consequences. The phenotypic characteristics of the initially described patients included CD4+ T cell lymphopenia, immune deficiency, EBV viremia, and EBV-related lymphoproliferative disease. To date, a total of 25 patients have been reported. The spectrum of the MAGT1 defect ranges from other viral infections (HSV, VZV, CMV, MCV) and sinopulmonary bacterial infections, autoimmune diseases, non-EBV driven lymphoproliferative disease, Castleman disease, HHV8+ Kaposi's sarcoma, vasculitis (Kawasaki) to glycosylation defects in new patients. Here, we report 2 patients from two different families with novel MAGT1 mutations and different clinical features. The first patient presented with B cell lymphoma and low IgM level without recurrent infections. The second patient presented with recurrent upper respiratory tract infections, Kawasaki-like disease, hypogammaglobulinemia, and T cell lymphopenia. X-MEN disease is the first phenotype identified due to MAGT1 mutation. The identification of new mutations and atypical presentations will clarify whether there is a relationship between the genotype and the phenotype and the characteristics of the disease. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/3111 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/3111/1798