Hyper IgM syndromes is a group of primary immune deficiency disorders characterized by defective CD40 signaling; via B cells affecting class switch recombination (CSR) and somatic hypermutation.

[7][1][2][3][12][4] 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.

This results in an overproduction of IgM antibodies and an underproduction of IgA, IgG, and IgE.

Additionally, anti-microbial therapy, use of granulocyte colony-stimulating factor, immunosuppressants, as well as other treatments, may be needed.