Which type of deficiency is commonly seen in hyper IgM syndrome?

Hyper IgM syndrome is primarily characterized by a defect in class switching in B cells. In a healthy immune response, B cells typically undergo class switching, enabling them to produce different classes of immunoglobulins such as IgG, IgA, and IgE in response to infections. However, in individuals with hyper IgM syndrome, this process is disrupted, leading to an abnormal accumulation of IgM with low or absent levels of other antibody isotypes.

The defect is often due to mutations affecting CD40 or its ligand (CD40L), which are critical for facilitating the interaction between T helper cells and B cells necessary for class switching. As a result, the immune system struggles to produce a diverse antibody response, increasing susceptibility to infections. This underlying mechanism is why class switching defect is the most accurate characterization of the deficiency seen in hyper IgM syndrome.

The other options do not accurately reflect the nature of the immunological dysfunction present in hyper IgM syndrome. IgM deficiency alone does not account for the presence of other immunoglobulins; complete B-cell deficiency would imply no B cells are functioning, and IgA deficiency does not align with the characteristic excess of IgM. Thus, the understanding of class switching defects provides insight into the immune challenges