Which of the following is a primary immunodeficiency disorder?

Explanation: The correct answer is b. DiGeorge syndrome. This disorder is caused by a deletion in chromosome 22, resulting in the underdevelopment of the thymus and parathyroid glands. It leads to impaired T cell function and is associated with developmental delays, chronic infections, and autoimmune problems.

Incorrect choices:

a. X-linked agammaglobulinemia is a primary immunodeficiency disorder that primarily affects B cell function, leading to a deficiency of immunoglobulins (antibodies).

c. Wiskott-Aldrich syndrome is an X-linked recessive disorder characterized by a triad of symptoms: eczema, thrombocytopenia (low platelet count), and immunodeficiency.

d. Severe combined immunodeficiency (SCID) is a group of rare disorders characterized by a severe deficiency of T cells, B cells, and natural killer (NK) cells.

Explanation: The correct answer is c. Common variable immunodeficiency (CVID) is characterized by a deficiency or absence of B cells, leading to a reduced ability to produce antibodies and an increased susceptibility to infections.

Incorrect choices:

a. DiGeorge syndrome is a disorder caused by a genetic defect resulting in the underdevelopment of the thymus and parathyroid glands, leading to T cell deficiency.

b. Severe combined immunodeficiency (SCID) is a severe form of immunodeficiency that affects both B and T cells, leading to a complete absence or dysfunction of the immune system.

d. Wiskott-Aldrich syndrome is a rare X-linked genetic disorder characterized by a triad of symptoms, including eczema, low platelet count, and immunodeficiency. It primarily affects T cells and platelets, not B cells.