Review Question - QID 106663

This patient is presenting with X-linked (Bruton's) agammaglobulinemia, which is an X-linked recessive disorder as demonstrated in Figure D.

X-linked (Bruton's) agammaglobulinemia is characterized by an absence of mature B cells and all immunoglobulins. It results from a defect in BTK, a tyrosine kinase gene on the sex X chromosome, which prevents B cell maturation. It presents with recurrent bacterial infections AFTER 6 months of age, when maternal IgG is no longer present. Typical laboratory findings include an absence of mature B cells and decreased immunoglobulins of all classes.

Reust reviews the evaluation of primary immunodeficiency diseases in children. He states when an immunodeficiency disease is suspected, initial laboratory screening should include a complete blood count with differential and measurement of serum immunoglobulin and complement levels. The presence of lymphocytopenia on complete blood count suggests a T-cell disorder, whereas a finding of neutropenia suggests a phagocytic disorder.

Ponader & Burger review the Bruton's tyrosine kinase (BTK) mutations in Bruton's agammaglobulinemia and the promise for therapeutic potential in targeting these mutations in autoimmune and B cell malignancies. Specifically, they discuss Ibrutinib (PCI-32765), a BTK inhibitor with therapeutic potential. Ibrutinib is currently in phase III clinical trials in patients with chronic lymphocytic leukemia and mantle-cell lymphoma.

Figures are described in the incorrect answer key below.

Incorrect Answers:
Answer 1: Figure A demonstrates an autosomal dominant mode of inheritance.
Answer 2: Figure B demonstrates a maternal mode of inheritance as is observed in mitochondrial disorders.
Answer 3: Figure C demonstrates an X-linked dominant mode of inheritance.
Answer 5: Figure E demonstrates an autosomal recessive mode of inheritance.