Hyper-IgM Syndrome

Hyper-IgM Syndrome is a rare immune system disorder that affects the body's ability to fight infections. It involves a problem with the immune cells that produce antibodies, which are proteins that help protect against germs. People with this condition have normal or high levels of one type of antibody called IgM, but very low levels of other important antibodies like IgG, IgA, and IgE. This imbalance makes it harder for the body to defend against bacteria, viruses, and fungi, leading to frequent and serious infections. The condition mainly affects the immune system, which is responsible for protecting the body from illness.

Hyper-IgM Syndrome is a primary immunodeficiency characterized by defective class-switch recombination in B cells, resulting in elevated or normal serum IgM levels with markedly decreased IgG, IgA, and IgE. The most common form is caused by mutations in the CD40LG gene encoding CD40 ligand on T cells, impairing T cell help for B cell isotype switching. This leads to defective humoral immunity and increased susceptibility to opportunistic infections, including Pneumocystis jirovecii pneumonia and recurrent sinopulmonary infections. The syndrome also involves impaired macrophage activation and defective cell-mediated immunity. Clinical significance includes increased risk of severe infections, autoimmune complications, and malignancies.