X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA), also known as Bruton agammaglobulinemia or Bruton disease, is a primary immunodeficiency disorder caused by mutations in the BTK (Bruton tyrosine kinase) gene located on the X chromosome. Because the condition is X-linked recessive, it predominantly affects males. The BTK protein is essential for the normal development and maturation of B lymphocytes, the white blood cells responsible for producing antibodies (immunoglobulins). In XLA, B-cell development is arrested at the pre-B-cell stage in the bone marrow, resulting in a near-complete absence of mature B cells in the blood and profoundly low or undetectable levels of all classes of immunoglobulins (IgG, IgA, IgM, IgE). Affected boys typically appear healthy during the first few months of life due to the protective effect of maternal antibodies transferred during pregnancy. Symptoms usually become apparent between 6 and 18 months of age as maternal antibody levels decline. Patients experience recurrent and often severe bacterial infections, particularly of the respiratory tract (sinusitis, otitis media, bronchitis, pneumonia), the gastrointestinal tract, skin, and joints. Common causative organisms include Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Patients are also susceptible to certain enteroviral infections, which can cause chronic meningoencephalitis, a serious and potentially fatal complication. Without treatment, recurrent pulmonary infections can lead to bronchiectasis and chronic lung disease. The mainstay of treatment is lifelong immunoglobulin replacement therapy (IgRT), administered either intravenously (IVIG) or subcutaneously (SCIG), which provides the antibodies the patient cannot produce. This therapy has dramatically improved survival and quality of life. Prompt and aggressive treatment of breakthrough infections with appropriate antibiotics is also essential. Patients should avoid live vaccines. With early diagnosis and consistent immunoglobulin replacement, most individuals with XLA can lead relatively normal lives, though vigilant monitoring for infections and lung function remains important throughout life. Hematopoietic stem cell transplantation and gene therapy are being explored as potential curative approaches but are not yet standard of care.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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