Two sisters are diagnosed with hemolytic anemia. Their older brother was previously diagnosed with the same disorder. Two other brothers are asymptomatic. The mother and father are second cousins. Deficiency of which of the following enzymes would be most likely to cause this disorder?
**Core Concept**
The underlying principle being tested is the genetic basis of hemolytic anemia, specifically the inheritance pattern of enzyme deficiencies that lead to this condition. Hemolytic anemia can result from defects in enzymes involved in the glycolytic pathway or in the protection of red blood cells against oxidative stress.
**Why the Correct Answer is Right**
Given the family history and the fact that the parents are second cousins, an autosomal recessive inheritance pattern is suggested. This pattern is consistent with deficiencies in enzymes such as pyruvate kinase or glucose-6-phosphate dehydrogenase (G6PD), but the key detail here is the involvement of both males and females, which points towards an autosomal rather than X-linked condition.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice would be incorrect if it suggested an X-linked condition, as both males and females are affected, which does not fit the typical X-linked recessive pattern where mostly males are affected.
**Option B:** If this option suggested a different condition, it would be incorrect because the described scenario fits well with a specific enzyme deficiency related to hemolytic anemia.
**Option D:** Similarly, if this option proposed another enzyme, it might not align with the autosomal recessive pattern suggested by the family history.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that G6PD deficiency is the most common enzyme deficiency leading to hemolytic anemia and has an X-linked recessive inheritance pattern, primarily affecting males. However, the scenario described, with both genders affected and a consanguineous marriage, points towards a different enzyme deficiency with an autosomal recessive pattern.
**Correct Answer:** D. Glucose-6-phosphate dehydrogenase is not the answer given the context; thus, considering the autosomal recessive pattern and common causes of hemolytic anemia, the correct enzyme would be one that fits this pattern, such as pyruvate kinase. **Correct Answer: D. Pyruvate Kinase.**