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Selective Antibody Deficiency With Normal Immunoglobulins (SADNI)

By

James Fernandez

, MD, PhD, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University

Last full review/revision Apr 2021| Content last modified Apr 2021
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Selective antibody deficiency with normal immunoglobulins (Ig) is characterized by deficient specific antibody response to polysaccharide antigens but not to protein antigens, despite normal or near normal serum levels of immunoglobulins, including IgG subclasses.

Selective antibody deficiency with normal immunoglobulins (SADNI) is a primary immunodeficiency disorder Primary Immunodeficiencies Immunodeficiency disorders are associated with or predispose patients to various complications, including infections, autoimmune disorders, and lymphomas and other cancers. Primary immunodeficiencies... read more . It is one of the most common immunodeficiencies that manifests with recurrent sinopulmonary infections. Selective antibody deficiencies can occur in other disorders, but SADNI is a primary disorder in which deficient response to polysaccharide antigens is the only abnormality (see table Humoral Immunity Deficiencies Humoral immunity deficiencies Immunodeficiency disorders are associated with or predispose patients to various complications, including infections, autoimmune disorders, and lymphomas and other cancers. Primary immunodeficiencies... read more ). The inheritance and pathophysiology have not been elucidated, but some evidence suggests that the cause may be inherited molecular abnormalities.

A subset of patients with SADNI initially have an appropriate response to polysaccharide antigen but lose antibody titers within 6 to 8 months (called SADNI memory phenotype).

Young children may have a form of SADNI that resolves spontaneously over time.

Diagnosis of SADNI

  • Immunoglobulin levels (IgG, IgA, IgM, and IgG subclasses)

  • Responses to polysaccharide vaccines

Because healthy children < 2 years can have recurrent sinopulmonary infections and weak responses to polysaccharide vaccines, testing for SADNI is not done unless patients are > 2 years. Then, levels of IgG, IgA, IgM, and IgG subclasses and responses to vaccines are measured. The only abnormality in laboratory testing is a deficient response to polysaccharide vaccines (eg, pneumococcal vaccine). Responses to protein vaccines are normal.

Treatment of SADNI

  • Pneumococcal conjugate vaccine

  • Sometimes prophylactic antibiotics and sometimes immune globulin replacement therapy

Sinopulmonary infections and atopic manifestations are treated aggressively. Uncommonly, when infections continue to recur, prophylactic antibiotics (eg, amoxicillin, trimethoprim/sulfamethoxazole) can be given.

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