## **Core Concept**
The question tests understanding of inherited disorders affecting the red blood cell (RBC) membrane, specifically those characterized by intrinsic cell wall defects. These defects lead to various types of anemia due to the compromised integrity and function of RBCs.

## **Why the Correct Answer is Right**
Hereditary spherocytosis is a disorder characterized by the production of red blood cells that are sphere-shaped rather than being biconcave disks. This condition results from mutations in genes that encode for proteins involved in the cytoskeleton of the RBC membrane, such as spectrin, ankyrin, band 3, and protein 4.2. These proteins are crucial for maintaining the structural integrity and flexibility of RBCs. The intrinsic cell wall defect in hereditary spherocytosis leads to premature destruction of RBCs (hemolysis), primarily in the spleen, due to their abnormal shape and decreased deformability.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Hereditary elliptocytosis is another disorder affecting the RBC membrane, but it is characterized by elliptically shaped RBCs rather than spherocytes. While it does involve intrinsic defects in RBC membrane proteins, the morphology of the RBCs is different.
- **Option B:** Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an enzyme deficiency that affects the pentose phosphate pathway in RBCs, leading to increased susceptibility to oxidative stress and hemolysis. However, it does not directly cause an intrinsic cell wall defect.
- **Option C:** Sickle cell disease results from a mutation in the hemoglobin gene, leading to abnormal hemoglobin (HbS) that polymerizes under low oxygen conditions, causing RBCs to assume a sickled shape. This condition affects the hemoglobin within RBCs rather than the cell membrane directly.

## **Clinical Pearl / High-Yield Fact**
A key clinical feature of hereditary spherocytosis is the presence of jaundice, splenomegaly, and often, gallstones due to chronic hemolysis. Laboratory findings typically include spherocytes on the peripheral blood smear, increased reticulocyte count, and elevated indirect bilirubin levels.

## **Correct Answer:** D. Hereditary spherocytosis.