A 37-year-old African-American woman is referred - resi_hopeful

[ArchivalUser]

A 37-year-old African-American woman is referred for prenatal genetic counseling because two of her sister's children have severe sickle cell anemia. The patient has never had a sickle cell crisis; subsequent physical examination does not demonstrate any major abnormalities. Genetic testing reveals that both she and her husband carry sickle cell trait.
Which of the following statements best describes the genetic defect underlying sickle cell anemia?

A.Deletion of the α-globin gene
B.Deletion of the β-globin gene
C.Point mutation in the α-globin gene
D.Point mutation in the β-globin gene
E.Point mutation in the γ-globin gene

[ArchivalUser]

cc

Please post explanations before locking topics...Its very important we see explanations or we can't learn from it.. Thanks

[ArchivalUser]

DD

[ArchivalUser]

D.

[ArchivalUser]

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[ArchivalUser]

The correct answer is D. 64% chose this.
On a genetic basis, sickle cell anemia is caused by a point mutation in the β-globin gene that changes the sixth amino acid from a glutamic acid residue to a valine residue. This change predisposes the sickle cell hemoglobin (HbS) to form insoluble polymers in the setting of hypoxia. Such polymerization results in an increased fragility of the RBC membrane and a tendency to hemolyze. Sickle cell anemia requires the inheritance of two mutated β-globin genes (ie, homozygosity).
A is not correct. 5% chose this.
The α-thalassemias are characterized by deletion (or missense mutation) of the α-globin gene. Healthy people inherit four copies of the α-globin gene (two from each parent). In the α-thalassemias, the severity of disease depends on the number of dysfunctional α-globin genes that are present.
B is not correct. 5% chose this.
The β-thalassemias are characterized by deletion (or missense mutation) of the β-globin gene. Healthy people inherit two copies of the β-globin gene (one from each parent). Patients with one functional β-globin gene (heterozygotes) have β-thalassemia trait, which is characterized by only a mild anemia. Patients with no functional β-globin genes have severe anemia and are often dependent on transfusions.
C is not correct. 19% chose this.
Sickle cell anemia is characterized by a specific point mutation in the β-globin (not α-globin) gene. A deletion or missense mutation of the α-globin gene will result in one of the α-thalassemias. The severity levels of the α-thalassemias are highly variable, depending mostly on the number of dysfunctional α-globin gene alleles that are inherited.
E is not correct. 7% chose this.
The γ-globin gene is involved in fetal hemoglobin (HbF, α-γ synthesis. In healthy patients the γ-globin gene is replaced by the β-globin gene shortly after birth, which coincides with the transition from HbF to adult hemoglobin (HbA).
Bottom Line:
Patients with sickle cell anemia have point mutations in both of their β-globin gene alleles. This point mutation predisposes the HbS molecule to polymerization in the setting of hypoxia, which predisposes RBCs to hemolysis and sickling.