ADA deficiency is associated with which primary immunodeficiency?

ADA deficiency is associated with which primary immunodeficiency?

• A. Acquired immunodeficiency syndrome
• B. DiGeorge syndrome
• C. Severe combined immunodeficiency
• D. Wiskott-Aldrich syndrome

Answer: (C)

The main concept here is that ADA deficiency causes a form of severe combined immunodeficiency. When adenosine deaminase is missing, toxic metabolites accumulate in lymphocytes and interfere with DNA synthesis, leading to failure of development and survival of both T and B cells (and often NK cells as well). This dual defect in cellular and humoral immunity is the hallmark of SCID, a primary immunodeficiency that presents early in life with severe, recurrent infections and poor growth. Other options don’t fit as the primary immunodeficiency in this context: AIDS is an acquired immunodeficiency caused by HIV, not a congenital condition; DiGeorge syndrome involves T-cell deficiency due to thymic hypoplasia from a 22q11 deletion but is not the ADA-related SCID; Wiskott-Aldrich syndrome features a triad of eczema, thrombocytopenia, and immunodeficiency but is a distinct genetic condition with different clinical clues.

The main concept here is that ADA deficiency causes a form of severe combined immunodeficiency. When adenosine deaminase is missing, toxic metabolites accumulate in lymphocytes and interfere with DNA synthesis, leading to failure of development and survival of both T and B cells (and often NK cells as well). This dual defect in cellular and humoral immunity is the hallmark of SCID, a primary immunodeficiency that presents early in life with severe, recurrent infections and poor growth.

Other options don’t fit as the primary immunodeficiency in this context: AIDS is an acquired immunodeficiency caused by HIV, not a congenital condition; DiGeorge syndrome involves T-cell deficiency due to thymic hypoplasia from a 22q11 deletion but is not the ADA-related SCID; Wiskott-Aldrich syndrome features a triad of eczema, thrombocytopenia, and immunodeficiency but is a distinct genetic condition with different clinical clues.