Which immunodeficiency is characterized by recurrent infections and low or absent immunoglobulin concentrations?

X-linked agammaglobulinemia is characterized by recurrent infections due to low or absent immunoglobulin concentrations. This condition is caused by a mutation in the BTK gene, which is essential for B-cell development. Individuals with this disorder have a significantly reduced number of B cells, leading to a deficiency in the production of antibodies. As a result, they are particularly susceptible to infections by encapsulated bacteria and certain viruses, which is a hallmark of this immunodeficiency.

In contrast, severe combined immunodeficiency (SCID) involves both T-cell and B-cell deficiencies and often presents with more severe, life-threatening infections from an early age. Hyper IgE syndrome is marked by elevated levels of IgE, not low immunoglobulin concentrations, and presents with recurrent skin and respiratory infections typically related to specific pathogens. Selective IgA deficiency involves the absence of IgA while other immunoglobulin levels may be normal; individuals may have increased susceptibility to mucosal infections but not the severe, recurrent infections seen in X-linked agammaglobulinemia.

Therefore, the defining features of X-linked agammaglobulinemia align perfectly with the question's description of a condition characterized by recurrent infections and low or absent immunoglob