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X-linked hyper IgM syndrome
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Reviewed April 2013
What is X-linked hyper IgM syndrome?
X-linked hyper IgM syndrome is a condition that affects the immune system and occurs almost exclusively in males. People with this disorder have abnormal levels of proteins called antibodies or immunoglobulins. Antibodies help protect the body against infection by attaching to specific foreign particles and germs, marking them for destruction. There are several classes of antibodies, and each one has a different function in the immune system. Although the name of this condition implies that affected individuals always have high levels of immunoglobulin M (IgM), some people have normal levels of this antibody. People with X-linked hyper IgM syndrome have low levels of three other classes of antibodies: immunoglobulin G (IgG), immunoglobulin A (IgA), and immunoglobulin E (IgE). The lack of certain antibody classes makes it difficult for people with this disorder to fight off infections.
Individuals with X-linked hyper IgM syndrome begin to develop frequent infections in infancy and early childhood. Common infections include pneumonia, sinus infections (sinusitis), and ear infections (otitis). Infections often cause these children to have chronic diarrhea and they fail to gain weight and grow at the expected rate (failure to thrive). Some people with X-linked hyper IgM syndrome have low levels of white blood cells called neutrophils (neutropenia). Affected individuals may develop autoimmune disorders, neurologic complications from brain and spinal cord (central nervous system) infections, liver disease, and gastrointestinal tumors. They also have an increased risk of lymphoma, which is a cancer of immune system cells.
The severity of X-linked hyper IgM syndrome varies among affected individuals, even among members of the same family. Without treatment, this condition can result in death during childhood or adolescence.
How common is X-linked hyper IgM syndrome?
X-linked hyper IgM syndrome is estimated to occur in 2 per million newborn boys.
What genes are related to X-linked hyper IgM syndrome?
Mutations in the CD40LG gene cause X-linked hyper IgM syndrome. This gene provides instructions for making a protein called CD40 ligand, which is found on the surface of immune system cells known as T cells. CD40 ligand attaches like a key in a lock to its receptor protein, which is located on the surface of immune system cells called B cells. B cells are involved in the production of antibodies, and initially they are able to make only IgM antibodies. When CD40 ligand and its receptor protein are connected, they trigger a series of chemical signals that instruct the B cell to start making IgG, IgA, or IgE antibodies.
CD40 ligand is also necessary for T cells to interact with other cells of the immune system, and it plays a key role in T cell differentiation (the process by which cells mature to carry out specific functions).
Mutations in the CD40LG gene lead to the production of an abnormal CD40 ligand or prevent production of this protein. If CD40 ligand does not attach to its receptor on B cells, these cells cannot produce IgG, IgA, or IgE antibodies. Mutations in the CD40LG gene also impair the T cell's ability to differentiate and interact with other immune system cells. People with X-linked hyper IgM syndrome are more susceptible to infections because they do not have a properly functioning immune system.
Read more about the CD40LG gene.
How do people inherit X-linked hyper IgM syndrome?
This condition is inherited in an X-linked recessive pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked recessive disorders much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
Where can I find information about diagnosis or management of X-linked hyper IgM syndrome?
These resources address the diagnosis or management of X-linked hyper IgM syndrome and may include treatment providers.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about X-linked hyper IgM syndrome?
You may find the following resources about X-linked hyper IgM syndrome helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for X-linked hyper IgM syndrome?
What if I still have specific questions about X-linked hyper IgM syndrome?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding X-linked hyper IgM syndrome?
antibody ; autoimmune ; cancer ; cell ; central nervous system ; chromosome ; chronic ; differentiation ; failure to thrive ; gastrointestinal ; gene ; immune system ; immunodeficiency ; immunoglobulin ; infection ; inheritance ; inherited ; ligand ; lymphoma ; mutation ; nervous system ; neurologic ; neutropenia ; neutrophils ; pneumonia ; protein ; receptor ; recessive ; sex chromosomes ; sinus ; sinusitis ; syndrome ; white blood cells ; X-linked recessive
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (8 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.