Tehran University of Medical Sciences Immunology and Genetics Journal 2645-4831 2 3 2019 09 01 147 152 Anahita Razaghian Department of Allergy and Clinical Immunology, Department of Pediatrics, Pediatrics Center of Excellence, Children's Medical Center, Tehran, University of Medical Sciences, Tehran, Iran Vahid Ziaee Pediatric Rheumatology Research Group, Rheumatology Research Center, Tehran University of Medical Science, Tehran, Iran Tooba Momen Department of Allergy and Clinical Immunology, Child Growth and Development Research Center, Research Institute for Primordial Prevention of Non-Communicable Disease, Isfahan University of Medical Sciences, Isfahan, Iran Mansoureh Shariat Department of Allergy and Clinical Immunology, Department of Pediatrics, Pediatrics Center of Excellence, Children's Medical Center, Tehran, University of Medical Sciences, Tehran, Iran 2019 07 19 Ataxia-telangiectasia is a rare primary immunodeficiency and multisystem DNA repair disorder which is caused by mutation in ataxia telangiectasia mutated (ATM) gene. The ATM protein plays a critical role in sensing DNA double-strand breaks (DSB), oxidative stress and other genetic stresses. The ATM can directly mention DNA ends in repair complexes and directly involved in the repair of DSBs induced during T cell and B cell rearrangement. Therefore, increase serum IgM level and recurrent infection mainly sinopulmonary, indistinguishable from hyper IgM syndrome can be a presentation of some AT patients. AT patients with class-switched defect are more prone to severe infections, autoimmunity and lymphoproliferative disorders. Herein we present an AT patient with characteristic feature of hyper IgM phenotype and lymphoproliferation is investigated. https://igj.tums.ac.ir/index.php/igj/article/view/34 https://igj.tums.ac.ir/index.php/igj/article/download/34/24