**Question:** True statements regarding hereditary spherocytosis are all of the following except: March 2012

A. Hereditary spherocytosis is a rare disease that affects less than 1 in 10,000 individuals.
B. Hereditary spherocytosis is a genetic disorder caused by mutations in the ankyrin gene.
C. Hereditary spherocytosis is a rare disease that affects more than 1 in 10,000 individuals.
D. Hereditary spherocytosis is a disease caused by mutations in the spectrin gene.

**Core Concept:** Hereditary spherocytosis is a rare autosomal dominant inherited disorder of erythrocyte membrane structure characterized by the presence of oval or spheroidal erythrocytes. The condition is caused by mutations in either the ANK1 gene (encoding for ankyrin) or SPTBN1 gene (encoding for β-spectrin). These mutations lead to impaired ankyrin-spectrin interaction, causing instability in erythrocyte membrane and hemolysis.

**Why the Correct Answer is Right:**

Correct answer D is incorrect because hereditary spherocytosis is primarily caused by mutations in the ANK1 gene (encoding for ankyrin) or SPTBN1 gene (encoding for β-spectrin). The mutations in these genes lead to impaired ankyrin-spectrin interaction, resulting in instability in erythrocyte membrane and hemolysis.

**Why Each Wrong Option is Incorrect:**

Option A is incorrect as the prevalence of hereditary spherocytosis is not specified in the question. It is a rare disease, but the exact prevalence is not provided.

Option C is incorrect because the prevalence is not specified and the statement is contradictory to the correct answer (D) that states it is a rare disease.

Option D is incorrect as mentioned above, due to the cause being mutations in ANK1 and SPTBN1 genes, not the spectrin gene.

**Clinical Pearl:** Hemolysis in hereditary spherocytosis is secondary to membrane instability caused by ankyrin-spectrin interaction impairment. In this condition, the red blood cells become oval or spheroidal due to mutations in the membrane proteins involved in maintaining the erythrocyte shape. This leads to premature breakdown (hemolysis) of red blood cells, causing anemia and increased reticulocyte production.