X-Linked Agammaglobulinemia (XLA) is a rare primary immunodeficiency.
Chromosome: Xq21.3-Xq22
Gene affected: Bruton's tyrosone kinase (BTK) gene
Action: signal transducer driving the final stages of B cell maturation, resulting of arrest of B cell development at the preB-cell stage.
Inheritance: X-linked (affects 50% of sons born to a carrier mother)
Clinical findings:
(1) history of recurrent bacterial infections, such as pneumonia, meningitis and sepsis
(2) at least 1 hospitalization for a bacterial infection prior to age 5 years
(3) poor humoral response to vaccines
(4) absence of tonsil and lymph nodes
Laboratory findings:
(1) serum levels of IgM, IgG and IgA are less than 2 SD below age-adjusted means
(2) less than 2% mature lymphocytes in the peripheral blood
(3) little or no increase in antibody titers 1 month after a protein or polysaccharide vaccine
(4) low or absent BTK protein
The diagnosis requires exclusion of other causes of immunodeficiency, especially autosomal recessive agammaglobulinemia.
