X-linked agammaglobulinemia (XLA; also known as Bruton’s agammaglobulinemia) is the name for a condition that affects the body’s abliity to make antibodies and fight infections. It belongs to a group of conditions known as antibody deficiencies. XLA affects only boys and its features include repeated episodes of bacterial infections affecting the ears, sinuses, nose, eyes, skin and the gastrointestinal tract (gut). It is a rare condition with about 5–10 people in a million affected.
Antibodies belong to a particular type of protein, called immunoglobulin, normally found in blood and tissue fluids. There are three majot types of immunoglobulin, known as:
- Immunoglobulin G (IgG) – the most abundant and common immunoglobulin, found in blood and tissue fluids. IgG functions mainlyagianst bacteria and soem viruses.
- Immunoglobulin A (IgA) – found in blood, tears and saliva. It protects the tissues of the respiratory, reproductive, urinary and digestive systems.
- Immunoglobulin M (IgM) – found in the blood. IgM functions in much the same way as IgG but is formed earlier in the immune response.
All types of immunoglobulin are made up of antibodies against the germs that an individual has met during the course of his or her life.
Antibodies are made by white blood cells called B-cells or sometimes referred to as B-lymphocytes. In XLA there are genetic changes known as mutations in the Bruton’s tyrosine kinase (BTK) gene. These mutations block the development of normal, mature B-cells that would normally make antibodies. As a result, people with XLA have very few mature B-cells and cannot make immunoglobulins; that is, the antibodies that are needed to protect the body against infections.
The aim of treatment in XLA is to replace the missing or defective antibodies with purified immunoglobulins from the blood of healthy donors in order to reduce the frequency and severity of infections. Although not a cure for XLA, immunoglobulin replacement therapy is often enough to keep patients healthy so that those affected can lead full and relatively normal lives. Children with XLA should take part in regular school activities, including exercise, and do not need to be limited in what they can do. It is important for the school to be aware of the diagnosis, however.
Antibiotics are often needed to treat breakthrough bacterial infections that will occur from time to time. A few individuals may need to take antibiotics every day to protect them from infection or to treat chronic sinusitis or chronic bronchitis. Patients with bronchiectasis (widening and scarring of the bronchial airways) may need help from a physiotherapist to help clear their airways.