Sickle Cell Disease (SCD) also known as Sickle Cell Anaemia (SCA) and Drepanocytosis is a hereditary blood disorder, characterized by an abnormality in the oxygen-carrying haemoglobin molecule in red blood cells. This leads to a propensity for the cells to assume an abnormal rigid, sickle-like shape under certain circumstances. Sickle cell disease occurs when a person inherits two abnormal copies of the haemoglobin gene, one from each parent. Seceral subtypes exist, depending on the exact mutation in each haemoglobin gene. Sickle cell is associated with a number of acute and chronic health problems, such as severe infraction, attacks of severe pain (Sickle Cell crisis) and stroke, and there is an increased risk of death. (Global Burden of Disease Study, 2013; Yawn et al, 2014).
According to National Heart, Lung and Blood Institute (NHLBI, 2013), Sickle Cell Anaemia is a blood disorder that causes abnormally shaped red blood cells. Normal blood cells are disk- shaped with an indentation in the centre, and they move smoothly through the blood vessels.
But with sickle anaemia, the body produces red blood cells that are shaped like a sickle, or crescent. These cells don’t move through the blood stream as easily and they tend to stick and clump together and cause other health complication. Sickle cell anaemia is just one of many forms of sickle cell disease. It is a condition that is passed along from parents to their children. This disease is more common in people of certain ethnicities, including blacks and Hospanics. In the same vein, Clinical Research on Sickle Cell Disease (CRSCD, 2014) stated that sickle cell disease is the most common inherited blood disorder which is caused by a mutation in the haemoglobin-beta gene found on chromosome II. Haemoglobin transports oxygen from the lungs to other parts of the body. Red blood cells with normal haemoglobin (hemoglobin A) are smooth and round and glide through blood vessels. In people with sickle cell disease, abnormal haemoglobin molecules – haemoglobin S – stick to one another and form long, rod-like structures. These structures caused red blood cell to become stiff, assuming a sickle-shape. Their shape causes these red blood cells to pile up, causing blockages and damaging vital organs and tissue.
Also, Welkom (2012) and Yanni et al., (2009), viewed Sickle Cell Disease as one of the most common childhood onset, single – gene disorders, affecting primarily people of African descent. The sickle cell gene causes an abnormality in the iron-rich protein haemoglobin that is responsible for carrying oxygen through the blood and giving blood its red colour. The abnormal haemoglobin causes cells to become “Sickle Shaped” resulting in irregular blood flow (National Heart Lung Blood Institute (NHLBI), 2010). The red blood cell can stick and block the flow of blood to the limbs and organs resulting in pain, organ damage and a low blood count. For one to inherit the disease, two copies of the sickle cell gene (i.e. one from each parent) must be transmitted to the offspring. Thus, children whose parents each carry the trait will have a 25% chance of inheriting the disease. In other words, Sickle Cell Disease (SCD) include a variety of pathological conditions resulting from the inheritance of the sickle haemoglobin (HBs) gene either homozygously or as a compound heterozygote with other interacting abnormal haemoglobin gene. The disease is clinically one of the most important haemoglobin opaties (Monika, 2008).
The most important protein of Red Blood Cells (RBCs) is haemoglobin which consists of four globin chains, each folded around a haem molecule. Haemoglobin delivers oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. The predominant haemoglobin in adulthood is HB A which consists of two Alpha and two Beta globin chains. Other haemoglobins are HbA2 and HbF. During itner-uterine development, several globin chains are synthesized with the predominant haemoglobin type during foetal life being Hb F in the first twelve (12) weeks after birth, the Hb F quickly declines, leaving HbA and Hb 2A as the remaining haemoglobins. The Beta globin gene is found in chromosome II.
A single point mutation in the 6th codon leads to substitution of glutamic acid for valine, resulting in an abnormal globin β s. this result in the formation of sickle haemoglobin or (Hbs). In Haemoglobin c (Hbc) the same codon is changed by the insertion of lysine. In Hb D, there is a replacement of glutamine for glutamic acid at position B 121, and in Hb0 the same codon is changed by the insertion of lysine. These haemoglobin, codon inherited with Hbs, result is clinically significant SCD. Sickle cell disease also results from the inheritance of Hbs with genes from β thalassanimias. The latter result from a wide variety of DNA mutation – that have in common a reduced synthesis of globin chains. The more severe syndrome called Sickle Cell
– β O thalassaemia with no HbA, less severe β thalassaemia mutations result in reduced but variable levels of B-chain synthesis and hence levels of HBA. The most common genotype is
homozygous SS disease. S Hemoglobin C (Sc) disease, SB+thalassaemia and SBO thalassaemia are also relatively common.
Furthermore, John (2009), also claimed that sickle cell disease is a serious disease in which the body makes sickle shaped red blood cells “Sickle-Shaped” means that the cells look like crescents instead of the normal disc shape. Under a microscope, normal red blood cells look like dough nuts without holes in the centre. They move easily through blood vessels. Red blood cells contain the iron-rich protein haemoglobin. This gives blood its red colour and carries oxygen from the lungs to the rest of the body. Sickle cells contain abnormal haemoglobin that causes the cells to become sticky and crescent shaped. When the haemoglobin release its oxygen. The stiff, sickle-shaped cells can stick to the lining of the blood vessels. This can damage the lining, creating a “danger” signal that attracts defensive cells. This response may enhance the “stickiness” and lead to more slowing of normal blood flow through the vessel. This reduces oxygen delivery to the tissue supplied by this part blocked vessel. People with sickle cell disease have a lower than normal number of red blood cells because sickle cells don’t live as long as normal cells after they leave the bone marrow.
Sickle cell usually die after about 10 to 20 days, compared to normal red blood cells, which live an average of 120 days. The bone marrow can’t make new red blood cells fast enough to replace all the dying ones. So this causes anaemia, low blood count that result in fatigue, shortness of breath and related symptoms. Because the cells are made normally, but die too rapidly, this is termed a “haemolytic” (destruction of red cells) anaemia.Download Full Material-N4000