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Sickle Cell Disease (SCD) also referred to as Sickle Cell Anemia (SCA) is an autosomal blood disorder that occurs in individuals who possess a pair of recessive Sickle Cell genes. Sickle Cell Disease is usually characterized by the abnormal appearance of the red blood cells (Alexander, Baldwin, Money & McDaniel, 2002). Ordinarily, the red blood cells with abnormal hemoglobin appear sickle-shaped, and this serves as an indication of presence of Sickle Cell Disease.
These sickle-shaped red blood cells are believed to display abnormal cell morphology and; therefore, they can be identified easily through medical diagnosis especially when sickling is caused by homozygous mutation (Metcalfe, 2008). Sickling of the red blood cells is believed to reduce flexibility of the affected cells because the sickle-cell shape is usually rigid: thus, transportation of oxygen is impaired.
Sickle Cell Disease occurs in three different forms depending on the nature of the inherited gene copies. It can occur in a homozygous form that means that an individual possesses two copies of hemoglobin S (HbSS), or it can occur in a heterozygous form. Heterozygous individuals possess two different copies of the ²-globin hemoglobin chains. They may have hemoglobin A pairing with hemoglobin S to form HbAS, and this is referred to as Sickle Cell Trait. Other heterozygous individuals possess Sickle-hemoglobin S paired with Sickle-hemoglobin C to form HbSC, a condition referred to as Thalasemia (Howe, 2007). However, it is worth noting that individuals with HbAS and HbSC are described as compound heterozygous because they do not display symptoms of the Sickle Cell Disease; since sickling of the red blood cells does not occur.
Gene mutation on chromosome 11has been identified to be the cause of the Sickle Cell Disease. Genes that are responsible for hemoglobin synthesis in human beings are found on chromosome 11; therefore, Sickle Cell Disease results from point mutations that occur on this chromosome. Ordinarily, gene mutations that occur on the chromosomal region that controls the synthesis of the ²-globin chain of hemoglobin results into formation of abnormal hemoglobin.
Gene mutation on chromosome 11 leads to amino acids mismatch at the sixth position of the ²-globin chain of hemoglobin. In this form of point mutation, glutamic acid that is usually found at the sixth position of the ²-globin chain of normal hemoglobin is replaced with valine (Metcalfe, 2008). This change in the structure of the ²-globin chain of hemoglobin results into distortion of the red blood cells morphology, and this serves as the principal reason as to why, the red blood cells in individuals with Sickle Cell Disease appear sickle-shaped.
The biochemical principle that leads into formation of the Sickle-cell shape of the red blood cells in individuals suffering from Sickle Cell Disease can be explained through, a physiological approach. It is believed that replacement of glutamic acid with valine amino acid results into the morphological changes that are observed on sickle cells (Howe, 2007). Glutamic acid is hydrophilic in nature: thus, it attracts water molecules, whereas valine is hydrophobic in nature. This means that the hydrophilic nature of hemoglobin is removed by replacing glutamic acid with valine amino acid; hence the orientation of hemoglobin is significantly influenced.
Sickling occurs due to the polymerization of the ²-globin chains of hemoglobin especially at the deoxygenated state. In the deoxygenated state, the abnormal ²-globin chains of hemoglobin form structures that create a patch at one end on the hemoglobin. Therefore, these patches fit into one another causing hemoglobin in the red blood cells to polymerize: thus, distorting the morphology of the red blood cells. Distortion of the red blood cells morphology causes them to assume a sickle-shape; hence the term sickling. This morphological distortion of the red blood cells structure has been found to reduce the red blood cells elasticity because; the distorted red blood cells do not resume the normal cell morphology, even after the restoration of oxygen levels in the intra-cellular fluid. Therefore, the polymerized red blood cells cannot pass through the narrow blood capillaries in the body tissues.
As a result, these abnormal red blood cells are destroyed through hemolysis leading anemic conditions that serve as the principal manifestation of the Sickle Cell Disease (Howe, 2007). However, it is worth noting that persistent anemia occurs because the rate of hematopoiesis in the bone marrow that is aimed at replacing the hemolyzed red blood cells is slower than the rate of the sickle-cell destruction. Moreover, individuals suffering from SCD experience Acute Chest Syndrome, stroke and Avascular Necrosis. Some of these conditions such as stroke occur as a result death of brain cells caused by inadequate oxygen supply.
Sickle Cell Disease is often diagnosed through microscopic examination of the red blood cells morphology, so as to identify the Sickle-shaped red blood cells through Sickle Cell Test (Alexander, Baldwin, Money & McDaniel, 2002). Additionally, amniocentesis can be carried out, so as to determine the nature of the hemoglobin gene copies in an individuals DNA.
Treatment of the Sickle Cell Disease is aimed at controlling the SCD symptoms; therefore, blood transfusion serves as the principal treatment approach. Moreover, medication with pain medicines such as Hydroxyurea is recommended for reducing pain episodes (Howe, 2007).
In a brief conclusion, SCD is a genetic blood disorder that is caused by mutation of the genes responsible for the synthesis of hemoglobin. Sickling of the red blood cells occurs due to polymerization of the ²-globin chains of hemoglobin, leading to hemolysis (Metcalfe, 2008). SCD is diagnosed through the Sickle Cell Test, and its treatment involves blood transfusion.
References
Alexander, J., Baldwin, M., Money, B. & McDaniel, G. (2002). Promoting, Applying, and Evaluating Problem-based Learning in the Undergraduate Nursing Curriculum. Nursing Education Perspectives, 23, 3-18.
Howe, E. (2007). Addressing Nature-of-Science Core Tenets with the History of Science: An Example with Sickle-Cell Anemia & Malaria. The American Biology Teacher, 69 (1), 5-23.
Metcalfe, D. (2008). The Role of Biological race in Understanding Genetic Disease. Mankind Quarterly, 48, 16-21.
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