Explanation: 👍 The correct answer is B. This boy most likely has Bruton agammaglobulinemia, which results from an X-linked defect in a tyrosine kinase required for the production of mature B lymphocytes. This disease is most often seen in boys (X linked) and is characterized by low levels of immunoglobulin of all isotypes (no mature B lymphocytes to produce the immunoglobulin). T lymphocyte number (CD4+ and CD8+ counts) is unaffected. The condition presents with recurrent bacterial infections after the age of 6 months, when the levels of maternal antibodies decrease.
👎 A is not correct. Ataxia-telangiectasia is a multisystem disorder caused by a defect in DNA repair enzymes. It manifests as neurologic impairment, ataxia, IgA deficiency, and telangiectasias of the eye and skin. CD4+ and CD8+ counts are not typically affected by this disease.
👎 C is not correct. Chronic granulomatous disease (CGD) results from a defect in the phagocytic ability of neutrophils. Therefore patients with CGD are more susceptible to infections by catalase-positive organisms such as Staphylococcus aureus and fungi. This disease does not affect immunoglobulin or T-lymphocyte levels. A rapid screening test for this disorder is a negative nitroblue tetrazolium dye reduction test. Further confirmatory testing for CGD involves immunoblotting and genetic testing.
👎 D is not correct. Job syndrome (hyper-IgE syndrome) is associated with the failure of helper T lymphocytes to produce interferon-y. Affected patients are FATED: coarse Facies, "cold," or noninflamed, skin lesions; Abscesses, retained primary Teeth, high IgE level, and Dermatologic problems (eczema). CD4+ and CD8+ counts are normally unaffected, but a decrease in CD8+ may also be seen.
👎 E is not correct. This answer is incorrect because all immunoglobulin classes are at low levels in this patient. Selective Ig deficiency is due to a defect in isotype switching. The most common selective immunoglobulin deficiency is IgA deficiency, which can lead to sinus and lung infections, diarrhea, and anaphylaxis on exposure to blood products with IgA. T-lymphocyte numbers are normal. 👎 F is not correct. Severe combined immunodeficiency (SCID) may result from a defective interleukin-2 receptor; adenosine deaminase deficiency, or failure to synthesize MHC class II antigens. SCID causes low levels of all immunoglobulin isotypes. It also profoundly reduces T-lymphocytes counts, which is in conflict with the results of flow cytometry in this case.
👎 A is not correct. Ataxia-telangiectasia is a multisystem disorder caused by a defect in DNA repair enzymes. It manifests as neurologic impairment, ataxia, IgA deficiency, and telangiectasias of the eye and skin. CD4+ and CD8+ counts are not typically affected by this disease.
👎 C is not correct. Chronic granulomatous disease (CGD) results from a defect in the phagocytic ability of neutrophils. Therefore patients with CGD are more susceptible to infections by catalase-positive organisms such as Staphylococcus aureus and fungi. This disease does not affect immunoglobulin or T-lymphocyte levels. A rapid screening test for this disorder is a negative nitroblue tetrazolium dye reduction test. Further confirmatory testing for CGD involves immunoblotting and genetic testing.
👎 D is not correct. Job syndrome (hyper-IgE syndrome) is associated with the failure of helper T lymphocytes to produce interferon-y. Affected patients are FATED: coarse Facies, "cold," or noninflamed, skin lesions; Abscesses, retained primary Teeth, high IgE level, and Dermatologic problems (eczema). CD4+ and CD8+ counts are normally unaffected, but a decrease in CD8+ may also be seen.
👎 E is not correct. This answer is incorrect because all immunoglobulin classes are at low levels in this patient. Selective Ig deficiency is due to a defect in isotype switching. The most common selective immunoglobulin deficiency is IgA deficiency, which can lead to sinus and lung infections, diarrhea, and anaphylaxis on exposure to blood products with IgA. T-lymphocyte numbers are normal. 👎 F is not correct. Severe combined immunodeficiency (SCID) may result from a defective interleukin-2 receptor; adenosine deaminase deficiency, or failure to synthesize MHC class II antigens. SCID causes low levels of all immunoglobulin isotypes. It also profoundly reduces T-lymphocytes counts, which is in conflict with the results of flow cytometry in this case.