Okay, let's tackle this question about Sickle Cell Anemia. The question is asking which statement is true except. So I need to figure out which option is the exception.

First, I remember that sickle cell anemia is a type of hemolytic anemia caused by a mutation in the beta-globin gene. This leads to the production of abnormal hemoglobin S, which causes red blood cells to become sickle-shaped under certain conditions. The key points about this disease include chronic hemolysis, vaso-occlusive crises, and the fact that it's an autosomal recessive disorder.

Now, the correct answer is supposed to be the exception. Let's think about common true statements. For example, it's true that sickle cell anemia leads to chronic hemolysis. It's also true that patients are more prone to infections, especially with encapsulated organisms like Streptococcus pneumoniae. Another true fact is that hydroxyurea is a treatment used to increase fetal hemoglobin production, reducing complications.

Wait, but which of these is an exception? Maybe one of the options refers to a false statement. For instance, if an option says that sickle cell anemia is caused by a defect in alpha-globin, that would be incorrect. Because the mutation is in the beta-globin gene. Alternatively, if an option claims that it's an autosomal dominant condition, that's wrong since it's autosomal recessive.

Another possible exception could be about the mode of inheritance. If an option states it's X-linked, that's incorrect. Also, if an option mentions that all patients have the same clinical presentation, that's false because there's a lot of variability. Or maybe a treatment that's not used for sickle cell anemia, like a drug specific to another condition.

I need to check each option. Since the options aren't provided, I'll focus on the core concepts. The key here is to identify which statement does not align with the known facts about sickle cell anemia. The correct answer would be the one that's an exception to the true statements.

**Core Concept**
Sickle cell anemia is an autosomal recessive hemoglobinopathy caused by a point mutation in the **β-globin gene** (GAG → GTG), leading to production of abnormal hemoglobin S (HbS). Deoxygenation causes HbS polymerization, sickling of RBCs, vaso-occlusion, and chronic hemolysis.

**Why the Correct Answer is Right**
The exception lies in a statement contradicting established pathophysiology. For example, if an option claims "Sickle cell anemia is caused by α-globin deficiency," this is incorrect because α-globin deficiency causes **α-thalassemia**, not sickle cell anemia. The β-globin mutation is central to sickle cell disease.

**Why Each Wrong Option is Incorrect**
**Option A:** If it states "Sickle cell anemia is autosomal dominant," this is wrong because the disease requires **two defective β-globin alleles** (homozygous) for full-blown disease.
**Option B:** If it claims "Hydroxyurea reduces sickling," this is correct (it increases fetal hemoglobin), so not the exception.
**Option C:** If it says "

✓ Correct Answer: D. Deletion of gene