Which genetic disorder is characterized by absence of functional B cells and is X-linked?

Bruton's agammaglobulinemia is an X-linked genetic disorder that leads to a significant deficiency in antibody production due to the absence of functional B cells. The disorder is caused by mutations in the BTK (Bruton tyrosine kinase) gene, which is critical for the development and maturation of B cells. As a result, individuals with this condition have extremely low levels of immunoglobulins (antibodies) and are highly susceptible to recurrent bacterial infections.

In this condition, the absence of functional B cells means the body cannot produce adequate immunoglobulins, which play a crucial role in the immune system by targeting pathogens for destruction. The characteristic feature is often observed in young boys, typically presenting with recurrent infections.

Other genetic disorders listed, while they may also impact the immune system, are not characterized specifically by the absence of functional B cells and do not follow the X-linked inheritance pattern associated with Bruton's agammaglobulinemia. For example, common variable immunodeficiency can show a range of defects in antibody production but is not solely due to the absence of B cells, and it is typically not inherited in an X-linked manner. Hyper-IgE syndrome and Wiskott-Aldrich syndrome involve