SCD is caused by a recessive, single-nucleotide mutation in the beta globin gene of Hgb. All of the following are TRUE about Sickle cell disease, EXCEPT:
**Core Concept**
Sickle cell disease (SCD) is a genetic disorder caused by a point mutation in the beta-globin gene of hemoglobin (Hgb), leading to the production of abnormal hemoglobin S (HbS). This mutation results in sickling of red blood cells under low oxygen conditions, causing various systemic complications.
**Why the Correct Answer is Right**
The correct answer will be the option that does not accurately describe a characteristic of SCD. The disease is indeed caused by a recessive, single-nucleotide mutation in the beta-globin gene of Hgb. The mutation leads to the substitution of glutamic acid with valine at position 6 of the beta-globin chain, resulting in the production of HbS. This abnormal hemoglobin polymerizes under low oxygen conditions, causing red blood cells to sickle and leading to vaso-occlusive crises, organ damage, and other complications.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because SCD is indeed caused by a recessive mutation. The disease is inherited in an autosomal recessive pattern, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to express the disease.
* **Option B:** This option is incorrect because the mutation in the beta-globin gene of Hgb is indeed a single-nucleotide mutation. It involves the substitution of a single nucleotide (adenine for glutamic acid) in the beta-globin gene, leading to the production of HbS.
* **Option C:** This option is incorrect because the disease is characterized by the production of abnormal hemoglobin S (HbS), not hemoglobin C (HbC). Hemoglobin C is a different type of hemoglobinopathy caused by a different mutation in the beta-globin gene.
* **Option D:** This option is incorrect because the disease is indeed characterized by the sickling of red blood cells under low oxygen conditions. The sickling of red blood cells is a hallmark of SCD and leads to various systemic complications.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that SCD is a genetic disorder that affects individuals of African, Mediterranean, and Middle Eastern descent. The disease is often diagnosed through a combination of clinical presentation, laboratory tests (such as hemoglobin electrophoresis), and genetic testing.
**Correct Answer:** C.