Amniocentesis conducted during genetic counseling of a pregnant woman reveals a fetal adenosine deaminase deficiency. This autosomal recessive immunodeficiency is usually associated with which of the following?
**Core Concept**
Adenosine deaminase (ADA) deficiency is a rare genetic disorder that affects the immune system, specifically the function of lymphocytes. It is an autosomal recessive disorder, meaning that a person inherits two defective copies of the ADA gene, one from each parent. This deficiency impairs the breakdown of adenosine and deoxyadenosine, leading to their accumulation and ultimately causing lymphocyte death.
**Why the Correct Answer is Right**
The ADA enzyme is crucial for the proper functioning of lymphocytes, particularly T and B cells. In ADA deficiency, the accumulation of toxic adenosine and deoxyadenosine compounds leads to the apoptosis (programmed cell death) of these lymphocytes. This results in a deficiency in both humoral (B cell-mediated) and cellular (T cell-mediated) immunity. Humoral immunity, which involves the production of antibodies by B cells, is impaired due to the lack of B cells. Cellular immunity, which involves the activation and proliferation of T cells, is also compromised, as T cells are also affected by the ADA deficiency.
**Why Each Wrong Option is Incorrect**
**Option A:** Humoral Immunity - Normal; Cellular Immunity - Normal. This is incorrect because ADA deficiency affects both humoral and cellular immunity, not just cellular immunity.
**Option B:** Humoral Immunity - Normal; Cellular Immunity - Deficient. This is incorrect because ADA deficiency affects both humoral and cellular immunity, not just cellular immunity.
**Option C:** Humoral Immunity - Deficient; Cellular Immunity - Normal. This is incorrect because ADA deficiency affects both humoral and cellular immunity, not just humoral immunity.
**Clinical Pearl / High-Yield Fact**
ADA deficiency is a rare but severe immunodeficiency that highlights the importance of proper immune function in preventing infections. It is often associated with severe combined immunodeficiency (SCID), a condition characterized by the inability to fight off infections due to the absence or dysfunction of both T and B cells.
✓ Correct Answer: D. Humoral Immunity - Deficient; Cellular Immunity - Deficient