Hyper IgM syndrome

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Hyper IgM syndrome is a family of genetic disorders in which the level of Immunoglobulin M (IgM) antibodies is relatively high. The disorder causes immunodeficiencies, including a higher than normal susceptibility to various types of infections. Individuals with hyper-IgM syndrome typically also have a low number of infection-fighting neutrophil cells.

IgM is the form of antibody that all B cells produce initially, before they undergo class switching due to exposure to a recognized antigen. Healthy B cells efficiently switch to other types of antibodies as needed to attack invading bacteria, viruses, and other pathogens. Generally, in people with hyper IgM syndromes, the B cells keep making IgM antibodies because they can't switch to a different kind of antibody. This results in an overproduction of IgM antibodies and an underproduction of all other types. Some hyper-IgM syndromes are actually deficiencies of the other immunoglobulin classes: IgA, IgG, and IgE.

Five types have been characterized:

  • Hyper-IgM syndrome type 2, characterized by mutations of the AICDA gene. In this type, B cells cannot recombine genetic material to change heavy chain production, which is a required step in switching classes.
  • Hyper-IgM syndrome type 3, characterized by mutations of the CD40 gene. In this type, B cells cannot receive the signal from T cells to switch classes.
  • Hyper-IgM syndrome type 4, which is a defect in class switch recombination downstream of the AICDA gene that does not impair Somatic Hyper Mutation.[1]
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