**Core Concept**
Adenosine deaminase (ADA) deficiency is a genetic disorder caused by the absence or malfunction of the enzyme adenosine deaminase, which plays a crucial role in the breakdown of adenosine and deoxyadenosine. This enzyme is essential for the proper functioning of the immune system.

**Why the Correct Answer is Right**
The deficiency of ADA leads to the accumulation of toxic compounds, such as deoxyadenosine triphosphate (dATP), which disrupts the normal functioning of lymphocytes, particularly T cells and B cells. This results in severe combined immunodeficiency (SCID), characterized by a weakened immune system, recurrent infections, and an inability to produce antibodies. The absence of ADA activity is responsible for the excessive proliferation of lymphocytes, leading to lymphopenia and the inability to mount an effective immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ADA deficiency is not primarily associated with glycogen storage diseases.
**Option B:** This option is incorrect because ADA is not directly involved in the regulation of blood pressure.
**Option C:** This option is incorrect because ADA deficiency is not typically linked to the development of cancer.

**Clinical Pearl / High-Yield Fact**
ADA deficiency is a rare but severe genetic disorder that highlights the importance of enzyme function in maintaining a healthy immune system. It is essential to diagnose and manage this condition promptly to prevent long-term complications and improve patient outcomes.

**Correct Answer: A. Severe Combined Immunodeficiency (SCID)**