An 8-month-old boy with a history of recurrent pneumonia is found to have almost no circulating IgG. Cellular immunity is normal. His brother had this same disease and died of echovirus encephalitis. His parents and sisters have normal serum levels of IgG. What is the appropriate diagnosis?

The congenital disorder - Bruton X-linked agammaglobulinemia appears in male infants at 5 to 8 months of age, the period during which maternal antibody levels begin to decline. The infant suffers from recurrent pyogenic infections and severe hypogammaglobulinemia. There is an absence of both mature B cells in peripheral blood and plasma cells in lymphoid tissues. Genetic defect:-Located on the long arm of the X chromosome, is an inactivating mutation of the gene for B-cell tyrosine kinase, an enzyme critical to B lymphocyte maturation. Other Options:- -Wiskott-Aldrich syndrome (choice C) is also an X-linked genetic disease but is characterized by defects in both B-cell and T-cell functions (i.e., humoral and cellular immunity). -DiGeorge syndrome (choice A) is a developmental disorder characterized by thymic and parathyroid aplasia. Diagnosis: X-linked agammaglobulinemia of Bruton