Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 20 3 2021 06 06 376 381 Seyed Alireza Mahdaviani Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Majid Marjani Clinical Tuberculosis and Epidemiology Research Centre, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Mahnaz Jamee Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran AND Pediatric Infections Research Center, Research Institute for Children’s Health, Shahid Beheshti University of Medical Sciences, Tehran, Iran Armin Khavandegar Student Research Committee, Alborz University of Medical Sciences, Karaj, Iran Hosseinali Ghaffaripour Clinical Tuberculosis and Epidemiology Research Centre, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Golnaz Eslamian Department of Immunology and Allergy, Mofid Children's Hospital, Shahid Beheshti University of Medical Science, Tehran, Iran Mehdi Ghaini Department of Immunology and Allergy, Mofid Children's Hospital, Shahid Beheshti University of Medical Science, Tehran, Iran Shabnam Eskandarzadeh Department of Immunology and Allergy, Mofid Children's Hospital, Shahid Beheshti University of Medical Science, Tehran, Iran Jean-Laurent Casanova Laboratory of Human Genetics of Infectious Diseases, Necker Branch, INSERM UMR 1163, Necker Hospital for Sick Children, University of Paris, Imagine Institute, Paris, France AND St. Giles Laboratory of Human Genetics of Infectious Diseases, Rockefeller Branch, The Rockefeller University, New York, USA AND Pediatric Hematology and Immunology Unit, Necker Hospital for Sick Children, AP-HP, Paris, France AND Howard Hughes Medical Institute, New York, USA Jacinta Bustamante Laboratory of Human Genetics of Infectious Diseases, Necker Branch, INSERM UMR 1163, Necker Hospital for Sick Children, University of Paris, Imagine Institute, Paris, France AND St. Giles Laboratory of Human Genetics of Infectious Diseases, Rockefeller Branch, The Rockefeller University, New York, USA AND Center for the Study of Primary Immunodeficiencies, Necker Hospital for Sick Children, AP-HP, Paris, France Davood Mansouri Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran AND Clinical Tuberculosis and Epidemiology Research Centre, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Ali Akbar Velayati Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran 2020 05 27 2021 01 11 Mendelian susceptibility to mycobacterial disease (MSMD) is a rare group of genetic disorders characterized by infections with weakly virulent environmental mycobacteria (EM) or Mycobacterium bovis bacillus Calmette-Guérin (BCG). Herein, we described the case of a 4.5-year-old boy with protein-losing enteropathy, lymphoproliferation, and candidiasis, who was found to have disseminated Mycobacterium simiae infection. A homozygous mutation in the IL12B gene, c.527_528delCT (p.S176Cfs*12) was identified, responsible for the complete IL-12p40 deficiency. He was resistant to anti-mycobacterial treatment and finally died due to sepsis-related complications. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/2845 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/2845/1688