*Review* **Diagnostic Challenges in Patients with Inborn Errors of Immunity with Different Manifestations of Immune Dysregulation**

**Karolina Pieniawska-Smiech ´ 1,2,\*, Gerard Pasternak 2,3, Aleksandra Lewandowicz-Uszy ´nska 2,3 and Marek Jutel 1,4,\***


**Abstract:** Inborn errors of immunity (IEI), formerly known as primary immunodeficiency disorders (PIDs), are inherited disorders caused by damaging germline variants in single genes, which result in increased susceptibility to infections and in allergic, autoimmune, autoinflammatory, nonmalignant lymphoproliferative, and neoplastic conditions. Along with well-known warning signs of PID, attention should be paid to signs of immune dysregulation, which seem to be equally important to susceptibility to infection in defining IEI. The modern diagnostics of IEI offer a variety of approaches but with some problems. The aim of this review is to discuss the diagnostic challenges in IEI patients in the context of an immune dysregulation background.

**Keywords:** allergy; autoimmunity; autoimmune lymphoproliferative syndrome; inborn errors of immunity; lymphoproliferation; malignancy; primary immunodeficiency
