What characterizes hyperIgM syndrome?

HyperIgM syndrome is characterized by an elevated level of immunoglobulin M (IgM) along with significantly reduced levels of immunoglobulin G (IgG) and immunoglobulin A (IgA). This condition is commonly linked to defects in class switching, which is essential for producing various types of antibodies necessary for effective immune responses. The underlying genetic factors can affect B cell function, preventing the proper maturation of B cells into plasma cells that generate these other immunoglobulin types.

Patients with hyperIgM syndrome often experience recurrent infections due to their inability to adequately produce IgG and IgA antibodies, which play critical roles in defending against a wide range of pathogens. Additionally, the high levels of IgM are a result of the body's compensatory mechanism in trying to mount an immune response despite the inability to produce other antibodies effectively.

The other scenarios do not align with the defining features of hyperIgM syndrome. For instance, elevated levels of IgG alongside low IgM would not indicate this syndrome, and a normal vaccine response suggests an adequately functioning immune system, which is not characteristic of hyperIgM syndrome. Furthermore, low IgM with normal antibody responses would also contradict the hallmarks of this condition. Therefore, the defining characteristic of hyper