Hyper-IgM syndromes are conditions in which the immune system fails to produce normal immunoglobulin A (IgA), IgG, and IgE antibodies but can produce normal or elevated IgM.
The hyper-IgM syndromes are caused by problems in communication between T cells and B cells, leading to B cells that do not mature properly and only produce IgM antibodies; production of other Ig antibodies requires T and B cell interaction. There are at least six genes that, when mutated, result in this syndrome. Four forms of hyper-IgM syndrome are recessive, and two are X-linked (disease caused by genes located on the X chromosome).
Infants with hyper-IgM syndromes usually develop significant respiratory infections within the first year of life. In some cases there also is a low neutrophil (type of white blood cell) count (called neutropenia) and an increased risk of unusual or opportunistic infections, such as Pneumocystis jiroveci pneumonia or chronic diarrhea from Cryptosporidium.
A doctor will consider hyper-IgM syndrome in people with unusual infections and low antibody levels. Normal numbers of T and B cells but elevated levels of IgM are very suggestive.
People with hyper-IgM syndrome should receive regular treatments of intravenous (through the vein) immunoglobulin or subcutaneous (just under the skin) immunoglobulin. Those with neutropenia may need granulocyte-colony stimulating factor (G-CSF) to stimulate the body to produce more white blood cells. Some also may need antibiotics to prevent pneumonia caused by the fungus Pneumocystis jiroveci.
Individuals with the X-linked form of the syndrome can be treated with a bone marrow transplant.