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X-linked agammaglobulinemia is characterized by low levels or absence of Igs and absence of B cells, leading to recurrent infections with encapsulated bacteria.
X-linked agammaglobulinemia results from mutations in a gene on the X chromosome that encodes Bruton tyrosine kinase (BTK). BTK is essential for B-cell development and maturation; without it, maturation stops before the B-cell stage resulting in no mature B cells and hence no antibodies.
As a result, male infants have very small tonsils and do not develop lymph nodes; they have recurrent pyogenic lung, sinus, and skin infections with encapsulated bacteria (eg, Streptococcus pneumoniae, Haemophilus influenzae). Patients are also susceptible to persistent CNS infections resulting from live-attenuated oral polio vaccine and from echoviruses and coxsackieviruses; these infections can also manifest as progressive dermatomyositis with or without encephalitis. Risk of infectious arthritis, bronchiectasis, and certain cancers is also increased.
With early diagnosis and appropriate treatment, prognosis is good unless CNS viral infections develop.
Diagnosis is by detecting low (at least 2 standard deviations below the mean) levels of Igs (IgG, IgA, IgM) and absent B cells (< 1% of all lymphocytes are CD19+ cells, detected by flow cytometry). Transient neutropenia may also be present.
Genetic testing can be used to confirm a diagnosis but is not required. It is usually recommended for 1st-degree relatives. If the mutation has been identified in family members, mutational analysis of chorionic villus, amniocentesis, or percutaneous umbilical cord blood samples can provide prenatal diagnosis.
* This is a professional Version *