Certified Pediatric Hematology Oncology Nurse (CPHON) Practice Exam

The primary characteristic of Sickle Cell Disease (SCD) is a mutation in the DNA that affects hemoglobin production. Specifically, SCD is caused by a genetic mutation in the HBB gene, which encodes the beta-globin subunit of hemoglobin. This mutation leads to the production of an abnormal form of hemoglobin known as hemoglobin S (HbS). Under conditions of low oxygen, hemoglobin S polymerizes, causing red blood cells to distort into a sickle shape. This sickled shape affects the cells' ability to navigate through blood vessels smoothly, leading to blockages, pain, and various complications associated with the disease.

The other options refer to aspects that may be related to hemoglobin but do not accurately encapsulate the primary characteristic of SCD. The deficiency of normal hemoglobin describes the consequence of the disease but does not specifically address the genetic mutation that is at the root of its cause. The presence of sickle-shaped red blood cells is a hallmark finding in SCD, but it arises because of the underlying mutation in hemoglobin, rather than defining the disease itself. The defect in white blood cell production is not directly relevant to SCD, which primarily affects red blood cells.