X-linked agammaglobulinemia (Bruton)
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A 9-month-old boy develops recurrent bacterial sinopulmonary infections after maternal antibodies wane. B cells are absent and all immunoglobulin classes are very low.
XLR; BTK (Bruton tyrosine kinase)
- Absent B cells (block in B cell development)
- Very low/absent immunoglobulins (all classes)
- Recurrent bacterial infections (after 6 months when maternal IgG wanes)
- Enteroviral infections (encephalitis)
- Small/absent tonsils and lymph nodes
- Flow cytometry: markedly reduced or absent CD19+ B cells (the hallmark)
- Immunoglobulin panel: very low/absent IgG, IgA, and IgM
- Flow cytometry shows reduced/absent BTK protein in monocytes; confirmatory molecular testing of BTK
- Carrier testing for at-risk female relatives
- Immunoglobulin replacement (lifelong)
"6ruton's": The "6" in 6 months looks like a "b" for Bruton's; symptoms appear after 6 months when maternal antibodies wane.
"Brutes must undergo pro-pr (proper) development": BTK mutation blocks B cell maturation from pro-B to pre-B cells. Bruton's has a "Proper" amount of pro-B cells but no mature B cells.
Bruton's has no tonsils ("brutonsils"): Absent lymphoid tissue (including tonsils) on exam because there are no B cells. Agammaglobulinemia = lack of gamma globulins (antibodies).