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Selective IgM deficiency

Individuals with selective IgM deficiency have low levels or lack immunoglobulin M (IgM) but have normal levels of IgA, and IgG. These individuals may have no illness, whereas others develop a variety of illnesses, including infections, allergies, and autoimmunity. 


IgM is the largest in size of all immunoglobulins. It is predominantly present in the circulating blood versus IgG, which is present both in the circulation and in the tissues, and IgA, which is predominantly in secretions. IgM is the first immunoglobulin secreted during an initial exposure to infectious organisms or a vaccine. IgM is also different from other immunoglobulins in that it contains five antibody molecules held together by the J chain. IgM antibodies serve as a first line of defense against bacteria, viruses, and fungi and in protection against autoimmune diseases and inflammation.

Although described more than 50 years ago, it is only recently that selective IgM deficiency has been included in the list of forms of PI. It is characterized by low (partial) to absent IgM (complete) in the blood but normal IgG and IgA levels. It occurs equally in children and adults and in both men and women. Partial selective IgM deficiency is more common than previously realized, whereas complete selective IgM deficiency is rare. 

Individuals with selective IgM deficiency, partial or complete, may not have any symptoms and, therefore, are unrecognized or undiagnosed. Those individuals who do have symptoms commonly suffer from infections, allergies, and autoimmune diseases. There is no specific treatment to correct low IgM levels; however, individuals who have this condition and also have impaired responses to vaccine antigens, particularly pneumococcal polysaccharide vaccines, may require immunoglobulin (Ig) replacement therapy

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Blood levels of IgM are low or absent, but IgA and IgG are normal. In some cases, IgG subclass deficiency may also be seen. One-third to one-half of individuals with selective IgM deficiency make poor responses to the Pneumovax-23 vaccine. Cellular immunity is normal. The phagocytic cell system and the complement system are also normal.

Clinical presentation

Individuals with selective IgM deficiency may be asymptomatic or symptomatic. Of those who are symptomatic, approximately 80% present with predominant bacterial infections. Among infections, the most common are chronic sinusitis, upper respiratory tract infections, bronchitis, and pneumonia. Occasionally cellulitis, sepsis, and meningitis have been observed. 

Almost 40% of individuals with selective IgM deficiency have allergic diseases, including hay fever and asthma. Autoimmune diseases are observed in about one-third of all individuals with selective IgM deficiency. Autoimmune diseases are more common in adults than children with selective IgM deficiency. Some common autoimmune diseases associated with selective IgM deficiency are systemic lupus erythematosus, rheumatoid arthritis, and autoimmune thrombocytopenia. Autoimmune diseases of endocrine glands, like Hashimoto’s thyroiditis and Addison’s disease, have also been seen in selective IgM deficiency. 


Since the symptoms of selective IgM deficiency are similar to other antibody deficiencies, such as common variable immunodeficiency (CVID) and selective IgA deficiency, selective IgM deficiency may be discovered when immunoglobulins are obtained to evaluate someone suspected of having a PI. Individuals are also identified when immunoglobulins are ordered for illnesses other than PI. 

The diagnosis of partial selective IgM deficiency is made if the serum IgM level is below two standard deviations of the mean for age-matched controls. Complete selective IgM deficiency is diagnosed with serum IgM levels < 5mg/dl. A definitive diagnosis of selective IgM deficiency, especially in children, should only be established after months of follow-up. Finally, to confirm a diagnosis of primary selective IgM deficiency, other possible causes of IgM deficiency must be excluded, such as leukemia, lymphoma, and immune suppressive medications, such as Clozapine. 

Prevalence and inheritance

The inheritance pattern of selective IgM deficiency is not known because family studies have not been done. Only a few families with selective IgM deficiency have been described. A prevalence of 3 in 10,000 for complete selective IgM deficiency and 3 in 1,000 for partial selective IgM deficiency in adults has been reported. However, large-scale and several-generation family studies are needed to determine the true inheritance and prevalence of selective IgM deficiency. 


The ideal treatment for selective IgM deficiency would be to replace IgM. However, no IgM-enriched immunoglobulin preparation is available in the U.S. Approximately one-third of individuals with selective IgM deficiency who have recurrent infections also have impaired IgG antibody response to vaccines. In such cases, Ig replacement therapy has been used and found to be beneficial. Recommendations for treating infections are similar to selective IgA deficiency; however, prophylactic use of antibiotics in selective IgM deficiency is generally not recommended. Allergic and autoimmune diseases are generally treated in a similar manner as those diseases in people without a PI. 


In the majority of reported cases, clinical presentation is mild; however, in some cases, meningitis and sepsis have been reported. Therefore, predicting long-term outcomes for individuals with selective IgM deficiency is difficult. Serious complications are rare. Although progression to other immunodeficiencies such as CVID has not been reported, long-term follow-up with individuals is still needed. Therefore, even people with mild symptoms should be followed every six months or annually and assessed to determine if there has been a progression to another immunodeficiency, as well as for the development of any complications such as autoimmune diseases.

This page contains general medical and/or legal information that cannot be applied safely to any individual case. Medical and/or legal knowledge and practice can change rapidly. Therefore, this page should not be used as a substitute for professional medical and/or legal advice.

Adapted from the IDF Patient & Family Handbook for Primary Immunodeficiency Diseases, Sixth Edition 
Copyright ©2019 by Immune Deficiency Foundation, USA