## **Core Concept**
A missense mutation is a type of point mutation where a single nucleotide change results in a codon that codes for a different amino acid. This change can lead to the synthesis of a protein with altered function. Missense mutations are significant because they can cause various genetic disorders depending on the protein affected.

## **Why the Correct Answer is Right**
The correct answer, **Sickle Cell Anemia**, is a classic example of a disease caused by a missense mutation. This condition results from a mutation in the HBB gene that codes for the beta-globin subunit of hemoglobin. The mutation leads to the substitution of glutamic acid (coded by GAG) with valine (coded by GTG) at position 6 of the beta-globin chain, resulting in sickle hemoglobin (HbS). This change causes red blood cells to assume a sickle shape under certain conditions, leading to the clinical manifestations of sickle cell anemia.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Cystic Fibrosis is primarily caused by a deletion mutation (ΔF508) in the CFTR gene, not a missense mutation. While some cases may involve missense mutations, the most common and classic mutation is a deletion.
- **Option B:** Thalassemia is a genetic disorder affecting hemoglobin synthesis, usually resulting from mutations that lead to reduced (beta-thalassemia minor) or absent (beta-thalassemia major) production of the beta-globin chains of hemoglobin. These are often frameshift or nonsense mutations rather than missense mutations.
- **Option D:** Huntington's Disease is caused by an expansion of a CAG repeat in the Huntingtin gene, leading to an elongated polyglutamine tract in the huntingtin protein. This is an example of a trinucleotide repeat disorder, not a missense mutation.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that sickle cell anemia is not only a classic example of a missense mutation but also a significant cause of morbidity and mortality worldwide. Early diagnosis and management can significantly improve outcomes. The sickle cell trait (HbAS) is generally protective against malaria, illustrating a classic example of heterozygote advantage.

## **Correct Answer:** C. Sickle Cell Anemia