page_title: Hyper-IgM syndrome type 3
section_title: Cause
hierarchical_section_title: Hyper-IgM syndrome type 3 / Cause
caption_attribution_description: Class_switch_recombination
context_page_description: Hyper-IgM syndrome type 3 is a form of hyper IgM syndrome characterized by mutations of the CD40 gene. In this type, Immature B cells cannot receive signal 2 from helper T cells which is necessary to mature into mature B cells.
context_section_description: Different genetic defects cause HIgM syndrome, the vast majority are inherited as an X-linked recessive genetic trait and most sufferers are male.
  IgM is the form of antibody that all B cells produce initially before they undergo class switching. Healthy B cells efficiently switch to other types of antibodies as needed to attack invading bacteria, viruses, and other pathogens. In people with hyper IgM syndromes, the B cells keep making IgM antibodies because can not switch to a different antibody. This results in an overproduction of IgM antibodies and an underproduction of IgA, IgG, and IgE.
caption: Class switch recombination
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