(See also Overview of Immunodeficiency Disorders.)
Hyper-IgM syndrome is characterized by normal or high levels of immunoglobulin M (IgM) and decreased levels or absence of other immunoglobulins. As a result, people are more susceptible to bacterial infections.
Children with hyper-IgM syndrome have frequent sinus and lung infections.
Doctors diagnose the disorder by measuring levels of immunoglobulins in the blood and by doing genetic tests.
Treatment involves immune globulin, antibiotics to prevent infections, and, when possible, stem cell transplantation.
Hyper-IgM syndrome is a primary immunodeficiency disorder. It may be inherited in one of the following ways:
How the disorder affects people varies depending on which gene is affected.
Levels of IgM may be high or normal. Other immunoglobulins may be absent, or levels may be low. The lack of other immunoglobulins makes people with hyper-IgM syndrome less able to fight off infections.
Most cases are X-linked. In X-linked hyper-IgM syndrome, B cells produce only IgM, not other types of immunoglobulin. Levels of IgM may be normal or high.
Infants with this form often develop pneumonia due to the fungus Pneumocystis jirovecii. Children have frequent sinus and lung infections during the first 2 years of life.
Many children die before puberty, and those who live longer often develop cirrhosis or lymphoma.
Doctors suspect hyper-IgM syndrome based on symptoms. They then measure levels of immunoglobulins. High or normal levels of IgM and low levels or absence of other immunoglobulins support the diagnosis.
When possible, the diagnosis is confirmed by genetic testing.
Prenatal genetic testing can be offered to women considering pregnancy if they have family members with certain gene mutations that can cause hyper-IgM syndrome.
People with hyper-IgM syndrome are usually given immune globulin to replace some of the missing immunoglobulins. Immune globulin consists of antibodies obtained from the blood of people with a normal immune system.
Some people with some forms of this syndrome are given trimethoprim/sulfamethoxazole (an antibiotic) to prevent Pneumocystis jirovecii infection.
Stem cell transplantation from a sibling with the same tissue type is done when possible.