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XLA, an X-linked recessive trait, is an inherited immunodeficiency resulting in an inability to produce B cells or immunoglobulin (antibodies). The mutated gene responsible (the Bruton tyrosine kinase or BTK) is located on the X chromosome.
Because males only have one X chromosome, they will be affected if they inherit the X chromosome containing mutated BTK. Females have two X chromosomes so are much less likely to be affected, but they may be carriers if they inherit the altered X chromosome.
XLA is also called by these names:
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X-linked recessive diseases are caused by genes located on the X chromosome. Although we have two copies of most genes, males have only one X chromosome and thus only one copy of genes on that X chromosome. If a male inherits a mutation in a disease-causing gene that is on the X chromosome, he will likely develop the disease.
A female will not usually develop an X-linked recessive disease because she has two X chromosomes, but she can be a “carrier.” She remains healthy because the normal gene on one X chromosome continues to function even though she carries the mutated gene on the other X chromosome, and she can pass the mutated gene on to her children.
For some X-linked recessive immunodeficiency diseases, carriers can be identified by laboratory tests. With others, a woman is discovered to be a carrier only after she gives birth to a child with the disease.
Adapted from chart in “Primary Immunodeficiency” NIH Pub. No. 99-4149, June 1999.
XLA is caused by mutations in the BTK gene found on the X chromosome. This gene normally produces a protein that is required for the development of B cells.
Signs and symptoms
Infants with XLA develop frequent infections of the ears, throat, lungs, and sinuses. Serious infections also can develop in the bloodstream, central nervous system, skin, and internal organs. These children tend to cope well with most short-term viral infections but are very susceptible to chronic viral infections such as hepatitis and polio.
They usually lack or have very small tonsils and adenoids.
People with XLA have extremely low numbers of circulating B cells, and blood tests show extremely low levels of all types of immunoglobulins (antibodies). They fail to develop antibodies to specific germs, for example, after immunizations. Most laboratories can look for B-cell numbers, which are very low in XLA. Specialized labs can test for the BTK mutation.
People with XLA receive intravenous (through the vein) immunoglobulin or subcutaneous (just under the skin) immunoglobulin regularly and antibiotics to treat infections.
Last Updated July 17, 2012
Last Reviewed October 15, 2010