The Sickle Cell Disease Biology Essay

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Blood is a connective tissue, which performs several important functions in our body. It is essential in maintaining our lives. Blood is involved in the transfer of oxygen and carbon dioxide among our body cells, maintaining our body temperature, delivering nutrients and waste products inside our body and also involved in our immunity system. The four main components of blood are red blood cells, white blood cells, plasma, and platelets. Plasma is the major component of blood, about 55% of the blood. Red blood cells, which constitute about 44% of whole blood are responsible in supplying oxygen to body cells. Platelets and white blood cells are taking up less than 1% of blood (The University Of Sidney, 2010). Normal red blood cells are biconcave disc-like shape. Oxygen is transported throughout the body by binding to the hemoglobin of red blood cells. Hemoglobin is a quaternary protein which consists of four iron-containing sites for the oxygen to bind with it (Anglin, M.R., 2012). Sickle cell disease is a blood related disorder. It is also an inherited genetic disease. It affects the hemoglobin molecule in the red blood cells. The abnormal hemoglobin cause the red blood cells to be rigid and losing its biconcave disc-like shape. Affected red blood cells are shaped like sickles or crescent moons (, 2011). Sickle Cell Disease

Picture 1: Shape of sickle red blood cell and normal red blood cell (National Human Genome Research Institute, 2010).

Millions of people throughout the world are affected by sickle cell anemia. This disease is particularly common among African, Spanish, Mediterranean, and indian ascestry (Health U.S.News, 2010). As sickle cell anemia is a genetically inherited disease, there are approximately 7% of the world population are carriers of this disease. 300,000-400,000 children affected by this disease are born every year (Roberts I., 2007). The Centers for Disease Control and Prevention estimated that about 90,000 to 100,000 of Americans are being affected by sickle cell anemia. About every 500 African-American baby born, one of them was affected by this disease (Centers for Disease Control and Prevention, 2011). Among the Americans, more than 2 million people have sickle cell trait while among African-Americans, in every 12 people, one of them is the carrier of the sickle cell gene (National Heart, Lung, and Blood Institute, 2012).

The sickle cell gene may be inherited by the next generation. The pattern of inheritance of sickle cell gene is called autosomal recessive inheritance. The child would be affected by sickle cell disease when both of the parents passed the sickle cell gene to the child. On the other hand, when only one of the parents passed this gene to the child, the child will have the sickle cell trait. The child with sickle cell trait will produce both normal hemoglobin and sickle cell hemoglobin. This child is considered as a carrier for this disease (Mayo Clinic, 2011). Although sickle cell disease cannot be prevented as the cause of this disease is the gene, parents can do premarital checkups to know their chances of having a child with sickle cell disease before having a baby. If both parents have sickle cell traits, there is a 25% chance for their child to have sickle cell disease. The chance for the child to have this disease will increase to 50% if one of the parents has this disease while another parent is a carrier for sickle cell gene. The child will not be affected by sickle cell disease if only one of the parents has sickle cell disease or is a carrier for this disease while another parent is normal (WebMD, 2010).

Sickle cell disease is caused by the structural abnormalities of hemoglobin due to the mutation in 6th position of β-globin chain gene. The glutamic acid codon is substituted by a valine codon (Micheal W.K.,PhD , 2013). The mutation of this gene will cause the production of sickle hemoglobin. The deoxygenated form of sickle hemoglobin is capable reversibly polymerizing with other sickle hemoglobin molecules. These polymers will distort the red blood cell into an elongated sickle shape. The sickling of red blood cell is initially reversible upon reoxygenation. However, after several repeated episodes of sickling, the membrane of the red blood cell will be damaged and cause the lost of K+ ions and water of the red blood cell. The red blood cell will eventually become rigid and reversible sickle shape. The life span of sickle cells is about 20 days which is much more shorter than the normal red blood cells which have life span of 120 days (Alvin H. and Schmaier L.M., 2003).

The patients with sickle cell disease might suffer various symptoms. Some are mild while some are severe. Some mild symptoms including fatigue, shortness of breath, dizziness, headache, coldness in hands and feet, pale skin colour, and chest pain. Among all these mild symptoms of sickle cell disease, fatigue is the most common symptom that suffer by the patients (National Marrow Donor Program, n.d.). Severe symptoms include chronic anemia, acute pain episodes, stroke, leg ulcer and many other symptoms. As the life span of sickle cells(20 days) is much shorter than normal red blood cells(120 days), the sickle cells die prematurely resulting in a chronic shortage of red blood cells to deliver oxygen to the whole body. Beyond that, sickle cells also have lower affinity to oxygen. The shortage of red blood cells and the low affinity between sickle cells and oxygen could also cause extreme fatigue, shortness of breath, dizziness, and delayed growth and development in children (Health U.S.News, 2010). Sickle cells might be stuck in small blood vessels causing obstruction in blood flow. This will eventually lead to sudden, periodic painful crises and tissues damage. The occur of leg ulcer is due to ischemia which will eventually lead to necrosis (Alvin H. and Schmaier L.M., 2003).Sickle Cell Anemia

Picture 2: The flow of sickle cells and normal red blood cells in blood vessel (MedIndia, n.d.).

The only cure for sickle cell disease is bone marrow transplantation but as we all known, it is difficult to find a matched donor and only small number of patient could have the chances to have this surgery (Hartree N., Dr., 2012). Besides that, there is also some other treatments available to reduce the effect suffered by patients. Therapy for crises such as hydration and pain medication can be used to reduce the degree of pain suffered by patients. While in some severe cases, blood transfusion could be done in order to increase the number of normal red blood cell when the body has no enough red blood cells to supply oxygen to the whole body. Apart from that, hydroxyurea, a medication which can increase the production of fetal hemoglobin can also be used. This drug will cause the body to produce fetal hemoglobin, which is the hemoglobin produced by baby inhibits the polymerization of sickle hemoglobin. This will eventually reduce the frequency of acute painful crises and the patient taking this medicine would not have to rely on blood transfusion as they have more red blood cell to carry oxygen to other part of their body (Alvin H. and Schmaier L.M., 2003).

As a conclusion, sickle cell disease is an inherited genetic disease that cannot be prevented and hard to be cure as the only cure is bone marrow transplantation. However, there are also other treatments that could help to reduce the suffer of the patients. Premarital checkups is also an important way to predict the possibility of the baby to be affected by sickle cell disease. The child that is affected by sickle cell disease should be looked after carefully. Sickle cell disease is not a fatal disease if the correct treatment is being taken. Be aware of the body condition and seek for doctor consultant if any of these symptoms showed.