Which type of immunodeficiency disorder is characterized by a defect in T cell function and is often associated with developmental delays, chronic infections, and autoimmune manifestations?

Explanation: The correct answer is d. Selective IgA deficiency. This disorder is characterized by a lack of immunoglobulin A, which can lead to an increased susceptibility to infections, particularly in the respiratory and gastrointestinal tracts.

Incorrect choices:

a. Selective IgM deficiency is a rare immunodeficiency disorder characterized by a lack of immunoglobulin M (IgM), not IgA.

b. X-linked agammaglobulinemia is a primary immunodeficiency disorder caused by a mutation in the BTK gene, resulting in a deficiency of B cells and immunoglobulins.

c. Common variable immunodeficiency (CVID) is a heterogeneous group of disorders characterized by decreased levels of immunoglobulins, including IgA, IgG, and IgM.

Explanation: The correct answer is b. X-linked agammaglobulinemia. X-linked agammaglobulinemia is a primary immunodeficiency disorder caused by a genetic mutation that leads to the absence of mature B cells, resulting in an inability to produce antibodies (immunoglobulins). As a result, individuals with this disorder are highly susceptible to infections, especially bacterial infections.

Incorrect choices:

a. DiGeorge syndrome is a primary immunodeficiency disorder characterized by abnormalities in the development of certain organs, including the thymus, leading to impaired T cell function.

c. Severe combined immunodeficiency (SCID) is a group of rare genetic disorders that affect both T cells and B cells, resulting in a severe impairment of the immune system.

d. Acquired immunodeficiency syndrome (AIDS) is a secondary immunodeficiency disorder caused by the human immunodeficiency virus (HIV) infection, which specifically targets and destroys CD4+ T cells, weakening the immune system's ability to fight infections.