Deficiencies that affect B cells are the most common primary immunodeficiencies and account for ~60-70% of all cases. Defective antibody production predisposes to invasive pyogenic bacterial infections as well as recurrent sinus and pulmonary infections. Complete lack of antibody production (agammaglobulinemia) predisposes to disseminated enteroviral infections causing meningoencephalitis, hepatitis, and a dermatomyositis-like disease. Diagnosis relies on the determination of serum Ig level.
- Agammaglobulinemia: Due to an X-linked mutation in the Bruton's tyrosine kinase (Btk) gene in 85% of cases.
- Hyper IgM: In most pts this syndrome results from an X-linked defect in the gene encoding CD40 ligand. Pts exhibit normal or increased serum IgM with low or absent IgG and IgA.
- Common variable immunodeficiency (CVID): Heterogeneous group of syndromes characterized by low serum levels of one or more Ig isotypes. Prevalence estimated to be 1 in 20,000. Besides infections, pts may develop lymphoproliferation, granulomatous lesions, colitis, antibody-mediated autoimmune diseases, and lymphomas.
- Isolated IgA deficiency: Most common immunodeficiency; affects 1 in 600 people. The majority of affected individuals do not have increased infections; antibodies against IgA may lead to anaphylaxis during transfusion of blood or plasma; may progress to CVID.
- Selective antibody deficiency to polysaccharide antigens.
Treatment: B Cell/Immunoglobulin Deficiency Syndromes IV immunoglobulin administration (only for pts who have recurrent bacterial infections and are deficient in IgG): - Starting dose 400-500 mg/kg given every 3-4 weeks
- Adjust dose to keep trough IgG level 800 mg/dL
- SC administration usually once a week can be considered in selected pts.
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