Misclassification of Ataxia Telangiectasia with Hyper IgM immune profile

Ataxia-telangiectasia is a rare primary immunodeficiency and multisystem DNA repair disorder, resulting from mutation in ataxia telangiectasia mutated (ATM) gene. The ATM protein plays a significant role in detecting DNA double-strand breaks (DSB), oxidative stress and other genetic stresses. The ATM can directly mention DNA ends in repair complexes and directly involve in the repairment of DSBs that are induced during T cell and B cell rearrangement. Therefore, increase in the level of serum IgM and mainly sinopulmonary recurrent infection, which is indistinguishable from hyper IgM syndrome, can be a symptom of some AT patients. AT patients with class-switched defect are more prone to severe infections, autoimmunity, and lymphoproliferative disorders. In this study an AT patient with characteristic features of hyper IgM phenotype and lymphoproliferation is investigated.