A nurse is explaining the etiology of sickle cell disease to a group of nursing students.
Which statement accurately describes the genetic basis of this condition?
A “Sickle cell disease results from a dominant genetic mutation.”..
B “Both parents must pass on the mutated gene for sickle cell disease to manifest.”..
C “The mutation in the HBB gene leads to the production of normal hemoglobin.”..
D “Sickle cell disease is inherited in an autosomal dominant manner.”..
The correct answer and Explanation is :
The correct statement is: B “Both parents must pass on the mutated gene for sickle cell disease to manifest.”
Explanation:
Sickle cell disease is a genetic disorder inherited in an autosomal recessive manner. This means that for a person to have sickle cell disease, they must inherit two copies of the mutated gene, one from each parent. The gene in question is the HBB gene, which provides instructions for making hemoglobin, the molecule in red blood cells that carries oxygen throughout the body.
Here’s a more detailed breakdown of the etiology:
- Genetic Basis:
Sickle cell disease is caused by a specific mutation in the HBB gene on chromosome 11. This mutation results in the production of abnormal hemoglobin, known as hemoglobin S (HbS). The normal version of the gene produces hemoglobin A (HbA), which allows red blood cells to remain flexible and disc-shaped. In sickle cell disease, the HbS causes red blood cells to become rigid and form a characteristic crescent or sickle shape. - Inheritance Pattern:
Since sickle cell disease is autosomal recessive, an individual must inherit two copies of the sickle cell mutation—one from each parent—to exhibit the disease. If an individual inherits only one copy of the mutated gene and one normal gene, they will be a carrier of the disease but will not exhibit symptoms. This carrier state is known as sickle cell trait. - Implications for Family:
For two carrier parents (each having one HbS and one HbA gene), there is a 25% chance with each pregnancy that the child will inherit both HbS genes and thus have sickle cell disease. There is a 50% chance the child will inherit one HbS gene and be a carrier, and a 25% chance the child will inherit both HbA genes and be neither a carrier nor affected by the disease.
In summary, sickle cell disease manifests only when an individual inherits two copies of the mutated gene, one from each parent. This autosomal recessive inheritance pattern is crucial for understanding both the risk of inheritance and the approach to genetic counseling.