Question

Why might you expect to find some Hb F in adults who are afflicted with sickle-cell anemia?

Short answer

Adults with sickle-cell anemia have some Hb F because it helps reduce the symptoms by interfering with the formation of sickle cells.

Step-by-step solution

Understanding Hemoglobin Types

Identify the types of hemoglobin present in humans. There are primarily three types: Hb A (adult hemoglobin), Hb A2 (a minor component of adult hemoglobin), and Hb F (fetal hemoglobin). The majority of hemoglobin in adults is Hb A.

Recognizing the Difference in Hemoglobin F (Hb F)

Understand that Hb F, which is the predominant hemoglobin in fetuses, has a higher affinity for oxygen compared to Hb A. Hb F is usually replaced by Hb A after birth, but some small amounts may persist into adulthood.

Connecting Hb F to Sickle-Cell Anemia

Explain that sickle-cell anemia is a genetic disorder affecting the beta-globin subunit of Hb A. Individuals with the disorder produce an abnormal form of hemoglobin known as Hb S, leading to deformed red blood cells. The presence of Hb F can interfere with the formation of sickle cells.

Why Hb F is Found in Adults with Sickle-Cell Anemia

Describe how increasing levels of Hb F can reduce the symptoms of sickle-cell anemia. Hb F does not participate in sickling and thus, the body may produce more Hb F as a compensatory mechanism to alleviate the effects of the mutated Hb S.

Key concepts

Hemoglobin Types

Hemoglobin is a vital protein in red blood cells responsible for carrying oxygen throughout the body. There are primarily three types of hemoglobin in humans:

• Hb A: The most abundant type in adults, consisting of two alpha and two beta chains.
• Hb A2: A minor component in adults, with two alpha and two delta chains.
• Hb F: Predominantly found in fetuses, made of two alpha and two gamma chains. This type has a higher oxygen affinity than Hb A.

While the majority of adult hemoglobin is Hb A, small quantities of Hb F may persist into adulthood.

Hb F (Fetal Hemoglobin)

Hb F is the primary hemoglobin produced by the fetus during pregnancy.
Its primary function is to efficiently transfer oxygen from the mother's blood to the developing baby, thanks to its higher affinity for oxygen compared to Hb A.
Usually, Hb F is replaced by Hb A shortly after birth. However, some adults retain a small amount of Hb F.
This presence of Hb F can be particularly important in certain medical conditions, such as sickle-cell anemia, where it can lessen the severity of symptoms.

Hb A (Adult Hemoglobin)

Hb A is the dominant form of hemoglobin found in adults.
It consists of two alpha and two beta-globin subunits and is responsible for transporting oxygen from the lungs to tissues and bringing carbon dioxide back for exhalation.
The orderly function of Hb A is crucial for the body's oxygen supply. Genetic disorders affecting the beta-globin subunit, such as sickle-cell anemia, can disrupt its function, leading to health issues.

Genetic Disorder

Sickle-cell anemia is a well-known genetic disorder that primarily impacts the production and function of hemoglobin.
This condition is caused by a mutation in the gene responsible for producing the beta-globin subunit of Hb A, resulting in the formation of an abnormal hemoglobin known as Hb S.
This mutation causes red blood cells to deform into a sickle shape, leading to various complications, such as pain, anemia, and organ damage.
Genetic disorders like sickle-cell anemia are inherited, meaning they are passed from parents to offspring.

Beta-Globin Subunit

The beta-globin subunit is a crucial part of the hemoglobin molecule, specifically in the Hb A type.
Each hemoglobin molecule consists of two alpha and two beta-globin chains.
In individuals with sickle-cell anemia, a mutation in the beta-globin gene leads to the production of an abnormal beta-globin subunit.
This abnormal subunit combines with alpha chains to form Hb S instead of the normal Hb A.
The altered shape and structure of Hb S result in the characteristic sickling of red blood cells, impacting oxygen transport and causing various health problems.