A patient with suspected Bruton's X-linked immunodeficiency syndrome would likely show a decrease in which test result?

Bruton's X-linked immunodeficiency syndrome, also known as X-linked agammaglobulinemia, specifically affects B-cell development. As a result, patients with this condition typically exhibit profoundly decreased levels of immunoglobulins, which include IgG, IgA, and IgM. This deficiency arises because B-lymphocytes are unable to mature into plasma cells that produce these antibodies.

In a patient with this syndrome, the absence of functional B-cells leads to a marked reduction in the secretion of immunoglobulins into the serum, which would be evident in laboratory serum tests. The condition does not significantly affect T-cells, which may still be present in normal or near-normal numbers. This distinguishes the finding of low immunoglobulin levels as a key indicator of this immunodeficiency.

The options that refer to T-cell counts or lymphocyte proliferation do not directly address the hallmark feature of Bruton's syndrome, which is the lack of antibody production due to B-cell deficiency. Therefore, assessing serum immunoglobulin levels highlights the critical immunological defect present in this particular syndrome.