**Question:** A patient of Mediterranean ancestry was given primaquine to protect against malaria when going on an overseas trip. The patient rapidly developed a hemolytic anemia due to a mostly silent mutation in which one of the following pathways or enzymes?

A. Glucose-6-phosphate dehydrogenase (G6PD) deficiency
B. Acetylcholinesterase deficiency
C. Aldolase deficiency
D. Alkaline phosphatase deficiency

**Correct Answer:** **Glucose-6-phosphate dehydrogenase (G6PD) deficiency**

**Core Concept:** Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an enzyme deficiency that affects the pentose phosphate pathway in red blood cells. This pathway is crucial for maintaining red blood cell stability and preventing oxidative stress. G6PD deficiency impairs the ability of red blood cells to withstand oxidative stress, making the cells more vulnerable to damage and hemolysis upon exposure to certain drugs or foods.

**Why the Correct Answer is Right:** Primaquine is an antimalarial drug that acts by inducing oxidative stress in the parasite, leading to its destruction. However, in patients with G6PD deficiency, their red blood cells are already susceptible to oxidative stress, rendering them prone to hemolysis upon primaquine exposure.

**Why Each Wrong Option is Incorrect:**

A. Acetylcholinesterase deficiency (Option B) is a rare disorder affecting acetylcholine levels, primarily impacting the neuromuscular junction and not red blood cells.

B. Aldolase deficiency (Option C) is a rare disorder affecting aldolase enzyme, which is crucial for glycolysis, but it does not involve oxidative stress or hemolysis.

C. Alkaline phosphatase deficiency (Option D) is a rare disorder affecting alkaline phosphatase enzyme, primarily impacting bone and liver, not hemolysis.

**Clinical Pearl:** It is crucial for medical professionals to consider G6PD deficiency when prescribing primaquine or other drugs that induce oxidative stress. This can prevent severe hemolysis and its complications in at-risk patients.