**Question:** Sickle cell anemia is characterized by: September 2010

A. Homozygous sickle cell anaemia
B. Homozygous sickle cell anaemia with severe anaemia
C. Polycythaemia
D. Hemolytic anaemia

**Core Concept:**
Sickle cell anemia is a genetic disorder caused by a mutation in the HBB gene, which encodes for beta-globin subunit of hemoglobin. This mutation leads to the production of abnormal hemoglobin S, causing red blood cells to become rigid and crescent-shaped, leading to reduced blood flow and increased risk of vessel occlusion. This results in various clinical manifestations, including chronic anemia, painful crises, and organ damage.

**Why the Correct Answer is Right:**
The correct answer is A: Homozygous sickle cell anaemia. Sickle cell anemia is characterized by the presence of two mutated HBB genes, resulting in the production of hemoglobin S (HbS). Homozygous sickle cell anaemia refers to the condition where an individual has two copies of the mutated HBB gene, leading to the development of sickle cell anaemia.

**Why Each Wrong Option is Incorrect:**

B: Homozygous sickle cell anaemia with severe anaemia - This description is incorrect because the severity of anemia in sickle cell anaemia is not solely determined by the presence of homozygous genotype. Other factors, such as inflammation, infection, and dehydration, can also contribute to severe anaemia.

C: Polycythaemia - This is incorrect because polycythaemia refers to an increase in red blood cell mass, which is typically seen in conditions like altitude-related polycythaemia or chronic renal failure. In sickle cell anaemia, the primary issue is the abnormal hemoglobin S, not increased red blood cell mass.

D: Hemolytic anaemia - This is incorrect because although sickle cell anaemia is characterized by hemolysis, it is not the primary feature of the disease. The primary abnormality is the production of hemoglobin S, which leads to red blood cell sickling and impaired oxygen transport, resulting in anaemia and other clinical manifestations.

**Clinical Pearl:**

Understanding the correct genotype and phenotype of sickle cell anaemia is crucial for accurate diagnosis and management. Homozygous sickle cell anaemia (AS genotype) is associated with severe anaemia, while heterozygous sickle cell trait (AS genotype) is characterized by mild anaemia and a protective mechanism against malaria. In homozygous genotype (AA genotype), there is no anaemia but individuals may experience recurrent pain crises due to sickling of red blood cells.