Hyper IgM syndrome
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The hyper-IgM syndrome is actually a family of genetic immunodeficiencies, as compared to the Acquired ImmunoDeficiency Syndrome (AIDS). In all types, the level of immunoglobulin M (IgM) is elevated or relatively normal. Some hyper-IgM syndromes are actually deficiencies of the other immunoglobulin classes IgA, IgG, and IgE. IgM is the constitutively expressed form of antibody that all B cells produce prior to class-switching after exposure to recognized antigen. Total neutrophil count is also typically low. Treatment includes IV-Ig infusion. Five types have been characterized:
Hyper IgM Syndrome Type 1, characterized by mutations of the CD40LG gene. T cells can't tell B cells to switch classes.
Hyper IgM Syndrome Type 2, characterized by mutations of the AICDA gene. B cells can't recombine genetic material to change heavy chain production, which a required step in switching classes.
Hyper IgM Syndrome Type 3, characterized by mutations of the CD40 gene. B cells can't receive the signal from T cells to switch classes.
Hyper IgM Syndrome Type 4, which is poorly characterized.
Hyper IgM Syndrome Type 5, characterized by mutations of the UNG gene.
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