Selective Antibody Deficiency With Normal Immunoglobulins (SADNI)
Selective antibody deficiency with normal immunoglobulins 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. 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: Overview of Immunodeficiency Disorders : Humoral immunity deficiencies). 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 mo (called SADNI memory phenotype).
Patients have recurrent sinopulmonary infections and sometimes manifestations that suggest atopy (eg, chronic rhinitis, atopic dermatitis, asthma). Severity of the disorder varies.
Young children may have a form of SADNI that resolves spontaneously over time.
Because healthy children < 2 yr can have recurrent sinopulmonary infections and weak responses to polysaccharide vaccines, testing for SADNI is not done unless patients are > 2 yr. 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.
Patients should be vaccinated with the pneumococcal conjugate (eg, 13-valent) vaccine.
Sinopulmonary infections and atopic manifestations are treated aggressively. Uncommonly, when infections continue to recur, prophylactic antibiotics (eg, amoxicillin, trimethoprim/sulfamethoxazole) can be given.
Rarely, when infections recur frequently despite prophylactic antibiotics, immune globulin replacement therapy can be given.