Introduction and Literature Review
Single gene disorders occur when a particular gene is known to cause the disease. Generally, they are initiated by DNA changes in a specific gene and habitually have expected inheritance outlines. Examples include sickle cell disorders and cystic fibrosis. Various inheritance patterns of single-gene diseases are predictable. DNA is continually subjected to mutations through accidental changes in its program. Alterations cause absent or misshapen proteins, and that leads to illness.
Single-gene disorders are divided into various categories. First, dominant diseases occur when a person has one mutant of a gene and a strong copy. Second, recessive ailments arise when individuals carry two alterations of the gene. Third, autosomal recessive occurs when both replicas of the mutated gene from one parent is donated to the child. They are, therefore, likely to develop the disorder. The parents are, thus, referred to as carriers of the disease. Sickle cell sickness is an example of autosomal recessive disease.
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Choice of Disease
The Sickle Cell Disorder
Sickle cell disease (SCD) comprises a group of disorders that affect hemoglobin. It is an inherited condition that causes the shortage and death of the red blood cells (RBCs). The hemoglobin is the molecule that transports oxygen throughout the body. Individuals suffering from this disease have hemoglobin S that changes the shape of the RBCs into an arced form and causes its rigidity. In America, most people living with the illness have Hispanic and African backgrounds.
The sickle-shaped cells are rigid; hence, they hardly change shape. They, therefore, burst apart as they move along the plasma vessels. In most cases, they only last ten to twenty days rather than the usual ninety to one hundred and twenty days. Consequently, the body experiences distress in generating new cells to substitute them, and therefore, an individual is likely to have small red blood cells hence causing anemia. Moreover, the crescent-shaped cells are trapped to vessel linings, triggering an obstruction that decelerates or halts the flow of plasma. Oxygen may, thus, fail to reach neighboring muscles. The absence of oxygen can initiate severe pain and exhaustion.
Description of the disease
Sickle cell diseases are initiated by modification of the hemoglobin beta (HBB) DNA, which provides instructions for making the subunit beta-globin. Its mutations, therefore, result in abnormality of the beta-globin, for example, hemoglobin E. Moreover, it causes low levels of the components leading to beta-thalassemia. People with SCD have one of the elements in hemoglobin that are substituted with hemoglobin S, for instance, hemoglobin C (Rees et al., 2010) . In sickle cell anemia, however, it changes both components of the hemoglobin. Additionally, in some individuals, mutations that yield hemoglobin S and beta-thalassemia may arise subsequently.
SCD is an autosomal recessive disorder; hence, duplicates of the gene in either cell have modifications. The parents of an individual with an autosomal recessive disorder each transfer one replica of the altered gene; however, they may not display any indications of the illness (Roy & Ganguly, 2013) . Individuals who carry only a copy of the sickle cell gene do not necessarily have the condition but may transfer the gene on to their offspring.
Various complications arise from the illness. Some people experience acute chest pains as the lungs are deprived of oxygen. Moreover, others indicate a pain crisis that mainly occurs when the sickle cells block the delivery of oxygen. Similarly, liver complications such as failure may occur as a result of blood vessel blockage; hence, adults may experience chronic pain. Gallstones are a common problem among people living with the disorder. They mainly occur when the bilirubin forms stones that get stuck in the gallbladder. Further, multiple blood transfusions lead to iron overload that consequently causes heart problems.
SCD also increases the chance of contracting infections such as chlamydia. Furthermore, the sickling of the RBCs result in the malfunctioning of the kidney, which may result in frequent and uncontrolled urination. The ailment increases the risk of high blood pressure and clots among pregnant mothers. In some cases, it results in eye problems on the retina as blood vessels are blocked and over bleed. In general, the main symptoms of SCD include anemia, delayed growth, and joint pains.
Gene Locus, Mutations, and Inheritance
The SCD is developed from a point mutation on the chromosome 11p15.5. The beta hemoglobin is created on the HBB found on the chromosome. A point substitution occurs when a single nucleotide base is altered, deleted, or inserted from a DNA or RNA sequence. It, therefore, affects the protein product. Point modification of the beta-globin causes the change of the hydrophilic amino acid glutamic acid to the hydrophobic amino acid valine (Renaudier, 2014) . Moreover, the deficiency of the amino acid at the sixth position of the beta-globin series, therefore, stimulates polymerization. The mutation, thus, changes the shape of the RBCs hence decreasing their efficiency and elasticity.
Additionally, a single point mutation of the chain causes sickle cell anemia; therefore, the nucleotide changes in the beta-globin results in severe pain when a part of the carrier is exerted. Generally, these mutations cause the HBB gene to transport low oxygen levels throughout the body. A normal HBB is transferred to a child when inherited from one parent. People who have one sickle cell trait are commonly healthy. If the parents have either the sickle cell trait or beta-thalassemia, their child is likely to develop SCD. Significantly, carriers of the gene are sheltered against malaria.
References
Rees, D. C., Williams, T. N., & Gladwin, M. T. (2010). Sickle-cell disease. The Lancet , 376 (9757), 2018-2031.
Renaudier, P. (2014). Sickle cell pathophysiology. Transfusion clinique et biologique: journal de la Societe francaise de transfusion sanguine , 21 (4-5), 178-181.
Roy, S., & Ganguly, S. (2013). Sickle Cell Anemia, an Autosomal Recessive Disorder: A Review. Int. J. Mol. Genet. , 3 , 63-67.
