*Review* **The Epidemiology and Clinical Presentations of Atopic Diseases in Selective IgA Deficiency**

**Izabela Morawska 1, Sara Kurkowska 2, Dominika B ˛ebnowska 3, Rafał Hrynkiewicz 3, Rafał Becht 4, Adam Michalski 1, Hanna Piwowarska-Bilska 2, Bozena Birkenfeld ˙ 2, Katarzyna Załuska-Ogryzek 5, Ewelina Grywalska 1, Jacek Roli ´nski <sup>1</sup> and Paulina Nied ´zwiedzka-Rystwej 3,\***


**Abstract:** Selective IgA deficiency (sIgAD) is the most common primary immunodeficiency disease (PID), with an estimated occurrence from about 1:3000 to even 1:150, depending on population. sIgAD is diagnosed in adults and children after the 4th year of age, with immunoglobulin A level below 0.07 g/L and normal levels of IgM and IgG. Usually, the disease remains undiagnosed throughout the patient's life, due to its frequent asymptomatic course. If symptomatic, sIgAD is connected to more frequent viral and bacterial infections of upper respiratory, urinary, and gastrointestinal tracts, as well as autoimmune and allergic diseases. Interestingly, it may also be associated with other PIDs, such as IgG subclasses deficiency or specific antibodies deficiency. Rarely sIgAD can evolve to common variable immunodeficiency disease (CVID). It should also be remembered that IgA deficiency may occur in the course of other conditions or result from their treatment. It is hypothesized that allergic diseases (e.g., eczema, rhinitis, asthma) are more common in patients diagnosed with this particular PID. Selective IgA deficiency, although usually mildly symptomatic, can be difficult for clinicians. The aim of the study is to summarize the connection between selective IgA deficiency and atopic diseases.

**Keywords:** atopic diseases; atopy; allergy; selective IgA deficiency; primary immunodeficiency
