Agammaglobulinemia, x-linked

X-linked agammaglobulinemia is caused by a change in the BTK gene. Genes are segments of DNA found on chromosomes. Genes produce specific proteins that the body needs to grow and work properly. When there is a change in a gene, the protein that the gene produces may be absent or not working properly. The BTK gene produces a protein called Bruton tyrosine kinase. This protein is important in the process of making B cells, which are a type of white blood cell. B cells mature into plasma cells, which produce antibodies. Antibodies are specialized proteins that help to protect the body from bacteria, virus and other foreign substances. When the Bruton tyrosine kinase protein is absent or not working properly, the body cannot make antibodies to fight infections, especially bacterial infections.