Misclassification of Ataxia Telangiectasia with Hyper IgM immune profile

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.