Sickle cell disease is best described as which of the following?

• A. A trait with increased red blood cell flexibility
• B. Individuals who are heterozygous for HbS with mild symptoms
• C. A disease caused by a deficiency of insulin
• D. Individuals homozygous for HbS; red blood cell destruction and episodic vascular blockage

Answer: (D)

Sickle cell disease is a genetic disorder caused by having two copies of the HbS allele, which changes the hemoglobin in red blood cells. When oxygen levels drop, HbS tends to polymerize and the red blood cells become rigid and sickle-shaped. These misshapen cells are fragile and break down faster than normal cells, leading to hemolytic anemia. They also tend to block small blood vessels, causing episodic pain and potential organ damage. That combination—two HbS alleles with red blood cell destruction and vascular blockages—is why this description fits best. The trait (one HbS allele) usually causes mild or no symptoms, and insulin deficiency is unrelated to sickle cell disease.