**Core Concept**
Sickle cell anaemia is a genetic disorder caused by a mutation in the HBB gene, leading to the production of abnormal haemoglobin (HbS). This abnormal haemoglobin causes red blood cells to assume a sickle shape under deoxygenated conditions, resulting in vaso-occlusive crises and other complications.

**Why the Correct Answer is Right**
The polymerization of haemoglobin is the key mechanism behind the sickling of red blood cells in sickle cell anaemia. When deoxygenated, HbS molecules aggregate and form long fibres that cause the red blood cells to lose their biconcave disc shape and adopt a characteristic sickle shape. This polymerization is mediated by the T-state of haemoglobin, which is stabilised by the substitution of glutamic acid with valine at position 6 of the beta-globin chain. The polymerization of HbS leads to increased rigidity of the red blood cells, which can cause them to become stuck in small blood vessels, leading to tissue damage and pain.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the pathophysiology of sickle cell anaemia.
* **Option B:** While haemoglobin is indeed involved in sickle cell anaemia, polymerization of haemoglobin is the specific mechanism that leads to sickling, not the accumulation of haemoglobin per se.
* **Option D:** This option is not directly related to the pathophysiology of sickle cell anaemia.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that sickle cell anaemia is more common in individuals of African descent, and its prevalence is higher in countries where malaria is endemic, due to the protective effect of HbS against malaria.

**Correct Answer:** C.