Introduction

Selective IgM deficiency (sIgMD) is a rare form of dysgammaglobulinemia, It is classified under primary humoral immunodeficiencies and characterized by low serum level of IgM, normal IgG and IgA levels with normal T cell numbers and function in the absence of a defined immunodeficiency. Pathogenesis of sIgMD is unknown, and no genetic or molecular basis has been defined yet. However, there are some hypothesis suggesting that it may be due to defective B cell maturation or T cell dysfunction [1, 2].
The European Society for Immunodeficiencies (ESID) Registry defines primary selective IgM deficiency (sIgMD) as serum IgM level repeatedly below 2 standard deviations (<-2SD) of reference levels, and normal levels of serum IgA, IgG and IgG subclasses, normal vaccination responses, absence of T cell defects and absence of causative external factors [3-5]. In another definition, sIgMD was defined as having low IgM, which is usually lower than 20 mg/dL in infants and children, or lower than 2SD. Usually, serum IgM levels are lower than10–20 mg/dL. The levels of other immunoglobulin isotypes are typically normal, although IgE may be increased [6, 7]. There is no definition for IgE, and high IgE may be observed in some cases [8]. SIgMD is observed in both children and adults [9].
Although it may occur in asymptomatic individuals [10], patients with sIgMD may present with various clinical features. It may associate with recurrent upper respiratory tract infections (URTI), atopic manifestations (rhinitis, asthma etc.), autoimmune diseases, malignancies, and other primary humoral immunodeficiency diseases. There are several reports in the medical literature including diseases that may cause decreased IgM levels, such as recurrent infections, autoimmune diseases (Celiac disease, hemolytic anemia), and different types of primary immunodeficiency (PID) (thymic hypoplasia, Wiskott Aldrich syndrome, ataxia telangiectasia, common variable immunodeficiency (CVID), Bruton agammaglobulinemia and congenital diseases (Bloom syndrome, Russel silver syndrome, DiGeorge syndrome) [11].
Our aim is evaluation of the demographic features, clinical presentations, associated diseases and infections of the patients who are followed up with sIgMD.