Heterozygous sickle cell anaemia gives protection against:
**Core Concept**
Sickle cell disease is an autosomal recessive disorder caused by a mutation in the HBB gene encoding the beta-globin subunit of hemoglobin. Heterozygous individuals, often referred to as sickle cell trait (HbAS), have one normal beta-globin gene and one mutated gene. This condition is not typically associated with symptoms but can provide protection against certain diseases.
**Why the Correct Answer is Right**
The correct answer is related to the fact that individuals with sickle cell trait have a selective advantage against malaria. This is because the mutated hemoglobin in sickle cell trait is toxic to the malaria parasite, Plasmodium falciparum, which is the most virulent species causing malaria in humans. The parasite is unable to infect red blood cells containing HbS, thereby reducing the risk of malaria infection in these individuals. This phenomenon is known as heterozygote advantage, where the heterozygous state provides a survival benefit in the presence of a particular disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** There is no evidence to suggest that sickle cell trait provides protection against tuberculosis.
* **Option B:** While sickle cell disease is associated with increased risk of infections, sickle cell trait does not provide protection against infections such as typhoid fever.
* **Option D:** There is no known association between sickle cell trait and protection against HIV infection.
**Clinical Pearl / High-Yield Fact**
Individuals with sickle cell trait are asymptomatic but can be asymptomatic carriers of the disease, and their children have a 50% chance of inheriting the mutated gene. Screening for sickle cell trait is recommended before blood transfusions or surgical procedures to prevent complications.
**Correct Answer: C. Malaria**