The Btk enzyme plays an essential role in the maturation of B cells in the bone marrow, and when mutated, immature pro-B lymphocytes are unable to develop into pre-B lymphocytes, which normally develop into mature (naive) B cells that leave the bone marrow into the blood stream.The disorder is inherited in an X-linked recessive fashion (as the gene linked to it is on the X chromosome) and is almost entirely limited to the sons of asymptomatic female carriers. This is because males have only one copy of the X chromosome, while females have two copies; one normal copy of an X chromosome can compensate for mutations in the other X chromosome, so they are less likely to be symptomatic.There is 30–50% chance of XLA patients having a positive family history of genetic inheritance. The rest of the cases occur as random mutations. If a carrier female gives birth to a male child, there is a 50% chance that the male will have XLA. A carrier female has a 25% chance overall of giving birth to an affected male child. An XLA patient will pass on the gene, and all of his daughters will be XLA carriers, meaning that any male grandchildren from an XLA patients daughters have a 50% chance of inheriting XLA. A female XLA patient can arise only as the child of an XLA patient and a carrier mother. XLA can also rarely result from a spontaneous mutation in the fetus of a non-carrier mother.
XLA patients, however, are apparently immune to the Epstein-Barr virus (EBV), as they lack mature B cells (and so HLA co-receptors) needed for the viral infection. Patients with XLA are also more likely to have a history of septic arthritis.It is not known if XLA patients are able to generate an allergic reaction, as they lack functional IgE antibodies. There is no special hazard for XLA patients in dealing with pets or outdoor activities. Unlike in other primary immunodeficiencies XLA patients are at no greater risk for developing autoimmune illnesses. Agammaglobulinemia (XLA) is similar to the primary immunodeficiency disorder Hypogammaglobulinemia (CVID), and their clinical conditions and treatment are almost identical. However, while XLA is a congenital disorder, with known genetic causes, CVID may occur in adulthood and its causes are not yet understood. In addition, to X-linked agammaglobulinemia a couple of autosomal recessive agammaglobulinemia gene mutations have been described including mutations in IGHM, IGLL1,  CD79A/B, BLNK  and deletion of the deletion of the terminal 14q32.33 chromosom.XLA was also historically mistaken as Severe Combined Immunodeficiency (SCID), a much more severe immune deficiency ("Bubble boys").A strain of laboratory mouse, XID, is used to study XLA. These mice have a mutated version of the mouse Btk gene, and exhibit a similar, yet milder, immune deficiency as in XLA. See also
Hypogammaglobulinemia (CVID)
Intravenous immunoglobulin (IVIg)

References
External links

GeneReviews/NCBI/NIH/UW entry on X-Linked Agammaglobulinemia