You are seeing a 4-year-old boy in clinic who is presenting with concern for a primary immune deficiency. He has an unremarkable birth history, but since the age of 6 months he has had recurrent otitis media, bacterial pneumonia, as well as two episodes of sinusitis, and four episodes of conjunctivitis. He has a maternal uncle who died from sepsis secondary to H. influenza pneumonia. If you drew blood work for diagnostic testing, which of the following would you expect to find?
1.Abnormally low number of B cells
2.Abnormally low number of T cells
3.Abnormally high number of B cells
4.Abnormally high number of T cells
5.Elevated immunoglobulin levels
sol:
This patient has X-linked (Bruton’s) agammaglobulinemia, which results in an abnormally low number of B cells.
X-Linked agammaglobulinemia (XLA) is an X-linked immunodeficiency resulting from a genetic defect in Bruton’s Tyrosine Kinase (BTK). This results in a defective signaling on B-cell precursor cells and prevents full differentiation and maturation of B cells. The lack of B cells leads to a lack of antibody production, and patients have recurrent bacterial infections. Symptoms typically start after 6 months (when the levels of maternal immunoglobulin have decreased). Unlike patients with Severe Combined Immunodeficiency (SCID), who typically die before the age of 1, patients with XLA are often able to have near-normal lifespans, with appropriate therapy (regular Immunoglobulin infusion).
Illustration A is a schematic of the maturation of lymphocytes and the immunodeficiency syndromes that result from defects at different points in the pathway.