X‑Linked Agammaglobulinemia — Pediatric Gastroenterology Review

Pathogenesis and genetics

Cause: Mutations in the Bruton* tyrosine kinase (BTK) gene leading to arrested B‑cell development and markedly reduced peripheral B cells.

Inheritance: X‑linked recessive; almost exclusively affects males.

Epidemiology and age at presentation

Incidence: Approximately 1:100,000 to 1:200,000 male births depending on cohort and ascertainment.

Typical onset: Clinical infections generally begin after 4–6 months of age as maternal IgG wanes; diagnosis may occur in infancy or early childhood.

Key laboratory findings

Immunoglobulins: Marked reduction in all immunoglobulin classes (IgG, IgA, IgM).
Peripheral B cells: Very low or absent CD19+/CD20+ B cells on flow cytometry.
Confirmatory testing: Genetic testing for BTK mutations supports diagnosis.

Typical clinical features

Recurrent bacterial infections: Predominantly sinopulmonary infections with encapsulated organisms; risk of progression to bronchiectasis if untreated.
Reduced lymphoid tissue: Small or absent tonsils and markedly reduced peripheral lymphoid tissue on exam.

Gastrointestinal manifestations

GI disease may be an important presenting or complicating feature.

Chronic diarrhea that can be persistent and severe.
Recurrent enteric infections: Giardia, Campylobacter, Cryptosporidium, and enteroviruses are commonly reported pathogens.
Bacterial overgrowth contributing to malabsorption and chronic symptoms.
Nodular lymphoid hyperplasia on endoscopy or histology.
Crohn‑like illness is uncommon but described; consider CVID and other immune defects in atypical IBD presentations.

Management

Immunoglobulin replacement therapy: Cornerstone of therapy (IVIG or subcutaneous Ig) to prevent infections and reduce morbidity.
Infection treatment: Prompt, pathogen‑directed antimicrobial therapy for enteric and systemic infections; consider longer or suppressive courses for chronic pathogens.
Supportive GI care: Manage malabsorption, treat small intestinal bacterial overgrowth, and address nutritional deficiencies.
Specialist coordination: Early referral to immunology and close coordination with gastroenterology, infectious disease, and, when needed, transplant/transfusion services.

Prognosis and follow-up

With regular immunoglobulin replacement and prompt infection management most patients survive into adulthood; ongoing surveillance for chronic lung disease, enteric complications, and rare malignancies is recommended.

Clinical pearls

Think XLA in male infants with recurrent bacterial infections beginning after 4–6 months and absent tonsils or lymphoid tissue.
Order flow cytometry for B‑cell markers (CD19/CD20) alongside quantitative immunoglobulins when XLA is suspected.
Coordinate care with immunology early to start Ig replacement and to guide infection prevention and GI management.

*Ogden C. Bruton was an American pediatrician who first described X‑linked agammaglobulinemia in 1952 and whose name was later given to Bruton tyrosine kinase; he had a long and distinguished military medical career in the U.S. Army, serving multiple tours including significant periods at Walter Reed Army Hospital and Tripler General Hospital. He organized the first military pediatric training program at Walter Reed Army Medical Center in 1949. He spearheaded efforts to improve health care for war brides and their children in Europe and served as a consultant to the Army Surgeon General before retiring from military service.