X-linked agammaglobulinemia (also called X-linked hypogammaglobulinemia, XLA, Bruton type agammaglobulinemia) is a rare X-linked genetic disorder that affects the body's ability to fight infection (origin of the name: A=no, gammaglobulin=Antibody).
Common symptoms of immunoglobulin deficiency appear after the infant is six months old. They include frequent ear and sinus infections, pneumonia, and gastroenteritis. Certain viruses, such as hepatitis and polio viruses, can also pose a threat. Children with XLA grow slowly, have small tonsils and lymph nodes, and may develop chronic skin infections. Approximately 20% of these children develop arthritis, possibly as a result of joint infections.
XLA is caused by a defect in the gene that codes for Btk. This defect leads to blocked maturation of B cells, the cells that produce immunoglobulins. Because other portions of the immune system are functional, people with XLA can fight off some types of infection, such as fungal and most viral infections. Immunoglobulins, however, are vital to combat bacterial infections. Infants with XLA usually do not show symptoms during the first six months of life because immunoglobulins from their mothers are circulating in their bloodstreams. As the mother's supply decreases, the baby becomes increasingly vulnerable to bacterial infections.
XLA diagnosis usually begins due to a history of recurrent infections, mostly in the respiratory tract, through childhood. The diagnosis is probable when blood tests show the complete lack of circulating B cells (determined by the B cell marker CD19 and/or CD20), as well as low levels of all antibody classes, including IgG, IgA, IgM, IgE and IgD. When XLA is suspected, it is possible to do a Western Blot test to determine whether the Btk protein is being expressed. Results of a genetic blood test confirm the diagnosis and will identify the specific Btk mutation,however its cost prohibits its use in routine screening for all pregnancies. Women with an XLA patient in their family should seek genetic counseling before pregnancy
The most common treatment for XLA is an intravenous infusion of immunoglobulin (IVIg, human IgG antibodies) every 3-4 weeks, for life. IVIg is a human product extracted and pooled from thousands of blood donations. IVIg does not cure XLA but increases the patient's lifespan and quality of life, by generating passive immunity, and boosting the immune system. With treatment, the number and severity of infections is reduced. With IVIg, XLA patients may a live relatively healthy life. A patient should attempt reaching a state where his IgG blood count exceeds 800 mg/kg. The dose is based on the patient's weight and IgG blood-count. The dosing rule of thumb is 1g of IVIg for every 2kg of patient's weight