Category: Sickle Cell Anemia

Oxidative Stress and Vascular Tone

The aberrant biochemistry of SCA promotes premature intravascular hemolysis. This occurs when sickled red cells release free hemoglobin polymers into the blood plasma via the free hemoglobin scavenging mechanism. This consequentially impairs the synthesis and circulation of nitric oxide thus impedes on vascular constriction( Rees, Williams, & Gladwin, 2010). Normal levels of nitric oxide maintain vascular tone by stimulating the vascular endothelium to relax. Accumulation of hemoglobin in the plasma are reported to be avid scavengers of nitric oxide thus reducing its bioavailability(Daves et al., 2019). Moreover, nitric oxide depletion is a precursor to vasospasms even in larger vessels. Inability to maintain a proper vascular tone attributes to SCA-related cerebrovascular disease, priapism and chronic leg ulcers(Kato, Steinberg, & Gladwin, 2017a). Progressive elevation of pulmonary vascular tone and vascular remodeling are also commonly manifested in individuals with SCA. In one study, 20 autopsies were performed on individuals with Hemoglobin S. It was reported that 75% of these individuals demonstrated signs of pulmonary hypertension (Haque et al., 2002).

Pharmaceutical prevention of intravascular hemolysis directly correlates with ameliorating clinically related outcomes. The sickle red cell release of oxygenated hemoglobin into the endothelium increases the risk of oxidative stress and induces intravascular hemolysis. Furthermore, the production and release of highly reactive ferric heme and iron in the blood plasma promotes the generation of hydroxyl radicals and ultimately oxidative damage((Fanis, Phylactides, Voskou, Kleanthous, & Aslan, 2015). In a 2019 study of 147 individuals, blood analysis via biochemical testing revealed an increased level of hydroxyl radicals and nitric oxide production prevalent in the SCD group. Aberrant blood element interactions not directly affected by the HbS mutation paves the way for ischemic reperfusion injury and supports elevated inflammatory tone(Kato et al., 2017a).

Evidence supports that alteration of hemoglobin capacity is a precursor to chronic inflammatory disease (Biswal et al., 2019). Studies that effectively target the reduction of oxidative and nitrosative stress in SCD remain in progression. Although proving the efficacy of nitric oxide inhalation therapy was unsuccessful(Ehman et al., 2017), a new therapeutic agent that deters oxidative stress has recently been the 1st FDA approved SCA-pathology targeting therapy since Hydroxyurea 30 years prior.

L-Glutamine is known for its increased uptake by sickled red cells in comparison to normal erythrocytes(Niihara, Zerez, Akiyama, & Tanaka, 1998). NAD+ uptake by cells slow oxidative damage hereby discouraging various clinical expressions. Although the pathologic mechanism is not fully understood, the efficacy of L-glutamine in reduction of VOC occurrences is an evidence-based phenomenon. In 2018, a double- blind phase 3 trial demonstrated a significant reduction in sickle cell related pain crises after receiving L-glutamine orally over the course of 48 weeks. A large portion of these participants were also noted as intolerable to hydroxyurea(New et al., 2018).

Targeting SCA Pathophysiology

Atypical Endothelial Interactions

Heterocellular aggregates are understood to propagate the phenomenon of vascular occlusion(Kau, Finnegan, & Barabino, 2009). The lifespan of an erythrocyte in a healthy individual is 120 days and is drastically shortened to 12 days in a person with sickle cell anemia; stimulating the increased production of reticulocytes rich in adhesion molecules. Both sickled erythrocytes and reticulocytes express more endothelial adhesion relative to normal erythrocytes (de Montalembert et al., 2014; Morikis et al., 2017). This phenomenon is attributed to the mechanistic role of extracellular matrix proteins and molecular interactions amongst blood formed elements and the vascular endothelium.

When Leukocyte concentrations rise, so does its tendency to adhere to the endothelium, platelets and each other. Modifying the expression of adhesion on cell endothelium is currently being investigated. Clinicians have studied ways to chemically block leukocytes and other adhesion mediated molecules in order to reduce blood viscosity and impede vasoocclusive pain episodes(VOC)(El Nemer et al., 2016; Molokie et al., 2017). Of note is the inhibition of the adhesion mediated molecule P-selectin, a molecule known for upregulation in endothelial cells. A placebo controlled, phase II experiment tested Crizanlizumab and its effectiveness; a

humanized antibody proven to bind to P-selectin and inhibit cell to cell related adhesion. A total of 198 adult patients were involved and those who received high dose Crizanlizumab resulted in a significant decline (62.9%) in sickle cell pain crisis(Friedrisch et al., 2016). Studies also support the benefit of an antiplatelet agent in treatment of sickle cell related complications.

Prasugrel functions to inhibit platelet activation and adenosine diphosphate mediated agglutination. The drug was studied in multiple phase 1 placebo controlled settings and demonstrated a reduction in platelet surface P-selectin in adults with SCA(Jakubowski et al., 2013; Wun et al., 2013)

Prevention of Erythrocyte Dehydration

Sickled erythrocyte dehydration plays an important role in diminished organ perfusion (Ballas et al., 2016). Maintenance of intracellular volume and proper ion concentrations is imminent in avoidance of erythrocyte dehydration. Yet it is a fate in repeated sickling. Several channels are critically involved but emphasis has been placed on the irregular functioning of the kalium-chloride cotransport system (KCC) and Gardos channel in SCA. KCC activity increases in proportion to repeated sickling; functioning pathologically in sickle cells to overshoot its target hemoglobin concentration and priming the reticulocyte to sickle(Lew et al., 2002). HbS polymerization activates a nonselective cation leaky pathway in a fraction of sickle cells upon deoxygenation. Calcium permeabilization promotes membrane protein digestion via activation of proteolytic enzymes like phospholipase and protease. One clinical investigation demonstrated a notable decline in erythrocyte KCC activity and permeabilization in the presence of magnesium intercellularly. Magnesium as an oral supplement for patients with sickle cell anemia demonstrated a notable improvement in erythrocyte dehydration (Fransechi et al., 1997).

Nevertheless, red blood cell magnesium levels, not serum magnesium is encouraged to be used as a determinant of SCA-related hospitalizations. Evidence shows that a patient with a lower concentration of erythrocyte magnesium strongly correlates with the increased risk of more frequent VOC episodes(Yousif, Hassan, & Al-Naama, 2018).

Although pharmacologically targeting the gardos channel in vitro has not been as successful as KCC modifications, a deepened understanding of its biochemistry has encouraged researchers to find efficient ways to upregulate potassium in SCA. Nevertheless, binding of upregulated vasoactive substance ET1, a potent vasoconstrictor, alters the mechanism of the gardos channel in an anoxic environment(Brugnara, 2018); Senicapoc is a gardos channel blocker that has been tested to increase intracellular potassium levels and counteract dehydration. In a phase II study, 145 patients received oral Senicapoc over the course of 52 weeks. Data showed a notable increase in hemoglobin levels and a reduction in dense erythrocytes (Ataga et al., 2011). Although the rate in which hemolysis improved relative to the placebo group was deemed insignificant, research is still in progress for pharmaceutically targeting erythrocyte dehydration for SCA.

Stem Cell Transplantation

Allogenic hematopoietic stem cell transplantation (HSCT) is the sole curative possibility for sickle cell patients who present with a severe clinical presentation. To date, human leukocyte antigen matched sibling donor (MSD) HSCT has the highest event free survival rates of 93- 97%(Gluckman, 2013). Reports show that transplant recipients have absolute resolution of their sickle cell related complications; including no further organ reperfusion damage or episodes of vasoocclusion (Roth, Krystal, Manwani, Driscoll, & Ricafort, 2012). Studies even report reduced levels in toxicities from 22.6% to 3% with the use of reduced-intensity conditioning regimens such as antithymocyte globulin (ATG) which limit the likelihood of organ transplant rejection (Margueritte et al., 2007).

Notwithstanding the success of allogenic MSD-HSCT, the donor pool for engraftment recipients remain low since only 20% of minorities have a matched sibling donor(Horan, Liesveld, Fenton, Blumberg, & Walters, 2005). The World Marrow Donor Association reports only 33% of African Americans having a match; attributed to having a less common more diverse haplotype. The battle continues in HSCT donor pool expansion although recent efforts in using alternative donor sources has demonstrated an encouraging outcome. Of note is matched unrelated donor (MUD) HSCT although mitigating occurrences of graft versus host disease remains limited with varied results. Walters et al reported a 1 to 2 year event free survival rates of 76% and 69% respectively and overall survival of 96% and 79% in recipients of Haploidentical HSCT. Moreover, rates of graft versus host disease (GVHD) were reported to be higher (62%) compared to having a related donor(Guilcher et al., 2018). The use of post- transplant cyclophosphamide which functions to impede alloreactive T cells in MUD HSCT has been recently used in a series of pilot studies to impede high levels of GVHD (Adamkiewicz et al., 2004). Bolanos et al was a study that used a haploidentical sibling, parent or child donor and cyclophosphamide as a non-myeloablative conditioning regimen which resulted in a 43% graft failure rate(Jones et al., 2012). Nevertheless, lack of larger studies on HSCT donor expansion and a standard criteria for donor recipients remain barriers treatment efficacy.

Conclusion

Although the genetic basis of sickle cell anemia is well reported, the quest for a deepened understanding of its complex pathogenesis continues. This has encouraged scientist globally to find ways in which therapeutic agents can target elements that exacerbate vasoocclusion and hemolysis. Understanding the roles of increasing HbF production, prevention of cellular and sickle red cell adhesion, inflammation, NO depletion and hemolysis have paved the for oral therapeutic advancements for SCD. Although there is a demand for more clinical trials and analysis, efforts toward producing effective treatment options that are available globally are at its all-time high.

Introduction

Haemoglobin is a word that was coined from two words “haemo” which means blood and “globin” meaning protein. Globin is a protein substance of four different polypeptide chains that have (141-146)amino acids. Haemoglobin is a conjugated globular protein. There are two important oxygenbinding proteins in vertebrates namely haemoglobin (Hb or Hgb) and myoglobin. Haemoglobin supplies oxygen (O2) to tissues. Haemoglobin’s function is to transport oxygen (O2) in the blood from the lungs to other tissues of the body and provide cells with the oxygen they need for foodstuff oxidative phosphorylation. Haemoglobin is found in the blood within erythrocytes (red blood cells (RBC)) and is the most common family of carriers of O2. Haemoglobin is the main component of red blood cells which number about 250 million per cell and its combination with iron (Fe) and oxygen forms the bright red colour of RBC. Haemoglobin comprises more than 95% of the erythrocyte, it also carries nitric oxide, which controls vascular tone and blood pressure. Haemoglobin is equally involved in the transport of respiratory carbon dioxide (about 20–25% of the haemoglobin as carbamino-haemoglobin) in which carbon dioxide is bound to the globin protein.

Erythrocytes further contain carbonic anhydrase, an enzyme that rapidly interconverts carbon dioxide and bicarbonate allowing the efficient transport of carbon dioxide, produced by respiration in the peripheral tissues, to the lungs, where it is exhaled. The haemoglobin combination with O2 and CO2 is reversible and this forms the basis for the gas-transport capability of hemoglobin. However, the combination of Hg with carbon monoxide (CO) is irreversible. This reduces the cell capacity to transport O2 during carbon monoxide poisoning. Myoglobin, the other O2-binding protein, stores oxygen in body tissues until cells need it. The highest levels of myoglobin are found in cardiac and skeletal muscles, which require large amounts of oxygen during contraction. Catabolism of haemoglobin splits off the globin portion into an amino acid pool while the haem portion is converted into biliverdin. In humans, biliverdin is converted to bilirubin and secreted in the bile. Iron from haem is however reused for haemoglobin synthesis. Haemoglobin is known to have an O2-binding capacity of 1.34 cm3 of dioxygen per gram which increases the total oxygen capacity in the blood by 70 times compared to dissolved oxygen in the blood. For normal level tissue oxygenation, an optimum haemoglobin level must be maintained. The normal Hb level for males is 14 to 18 g/dl, and for females it is 12 to 16 g/dl. A low level of haemoglobin results in anaemia, while a level above the normal is called erythrocytosis. Myoglobin and haemoglobin describe both protein structure-function relationships and the molecular basis of genetic diseases such as hereditary persistence of foetal haemoglobin, thalassaemias and sickle cell anaemia. Haemoglobin has a quaternary structure, it is a tetrameric protein with two α chains and two β chains (α2β2), each with a haem unit as a prosthetic group, each polypeptide chain having a very strongly three-dimensional structure similar to the unique polypeptide chain in myoglobin. However, their amino acid sequences differ by 83%.

Haemoglobin comprise two identical pairs of polypeptide chains, i.e. Two identical alpha (α) chains encoded on chromosome 16 containing 141 amino acids and two identical non-α chains (beta (β), gamma (γ) or delta (δ)chains)that encoded on chromosome 11.

• Hemoglobin A (Adult Hb): makes up about 95%-98% of hemoglobin found in adults; it contains two alpha (α) chains and two beta (β) protein chains(α2β2).
• Hemoglobin A2 (minor Adult Hb): makes up about 2%-3% of hemoglobin found in adults; it has two alpha (α) and two delta (δ) protein chains(α2δ2).
• Hemoglobin F (Hb F, fetal hemoglobin): makes up to 1%-2% of hemoglobin found in adults; it has two alpha (α) and two gamma (γ) protein chains (α2γ2). It is the primary hemoglobin produced by the fetus during pregnancy; its production usually falls shortly after birth and reaches adult level within 1-2 years.

Hemoglobin has two conformational states:

• T-state(Tense): the deoxy form of hemoglobin (lacks an oxygen species) and is also known as ‘deoxyhemoglobin”.
• R-state(Relaxed):is the fully oxygenated form: ‘oxyhemoglobin’.

Hemoglobinopathy

Hemoglobinopathy is a group of disorders in which there is abnormal production or structure of the hemoglobin molecule. It is passed down through families (inherited). This group of disorders includes hemoglobin C disease, hemoglobin S-C disease, sickle cell anemia, and thalassemias.

• AA= two normal beta globin genes
• SS= two sickle cell beta globin genes
• AS/SA= one normal beta globin gene and one sickle cell beta globin gene

Sickle Cell disease

Sickle cell syndromes are hereditary hemoglobinopathies. Homozygous sickle cell anemia (HbSS, autosomal recessive) is the most common variant of the sickle cell syndromes. Sickle cell trait is asymptomatic occurs in heterozygous carriers (HbSA). Other rare variants of sickle cell syndrome occur in individuals with one HbS allele and one other allele (HbC or Hb-β thalassemia). A point mutation in the beta chain of hemoglobin leads to substitution of glutamic acid by valine, thus changing the structure (and properties) of hemoglobin. Abnormal hemoglobin polymerizes when deoxygenated, resulting in sickle-shaped erythrocytes, which cause vascular occlusion and ischemia.

Distribution

Sickle cell disease (SCD) affects millions of people throughout the world and is particularly common in America among those whose ancestors came from sub-Saharan Africa; Spanish-speaking regions in the Western Hemisphere (South America, the Caribbean, and Central America); Saudi Arabia; India; and Mediterranean countries such as Turkey, Greece, and Italy. Predominantly individuals of African and East Mediterranean. Africa has the highest prevalence of the disease (30% heterozygote prevalence).

HbS gene is carried by 8% of the African American population. Sickle cell anemia is the most common form of intrinsic hemolytic anemia world wide Sickle cell disease occurs more often among people from parts of the world where malaria is or was common. It is believed that people who carry the sickle cell trait are less likely to have severe forms of malaria.

Clinical Presentations

Signs and symptoms of sickle cell anemia usually appear between 4-6 months of age. They vary from person to person and change over time. When HbS is deoxygenated, the Hb molecules polymerise and the red cell membrane becomes distorted, producing characteristic sickle-shaped cells. Sickling is precipitated by hypoxia, dehydration and infection. Sickled cells have a shortened survival and plug vessels in the microcirculation. This results in a number of acute syndromes termed ‘crises’ and chronic organ damage.

Vaso-occlusive crisis: Plugging of small vessels in the bone results in avascular necrosis, producing acute severe bone pain. Commonly affected sites include the femur, humerus, ribs, pelvis and vertebrae. Vaso-occlusion in the spleen can give rise to recurrent splenic infarction and adults may have no functional spleen. Occlusion at other sites can result in cerebrovascular accidents and proliferative retinopathy.

• Sickle chest syndrome: This may follow on from a vaso-occlusive crisis and is the most common cause of death in adult sickle disease. Bone marrow infarction results in fat emboli to the lungs, which cause sickling and infarction, leading to ventilatory failure.
• Sequestration crisis: Thrombosis of the venous outflow from an organ causes loss of function and acute painful enlargement. Massive splenic enlargement may result in severe anaemia and circulatory collapse. Sequestration in the liver leads to severe pain due to capsular stretching.
• Aplastic crisis: Infection with parvovirus B19 results in severe red cell aplasia, producing a very low Hb.

Investigations

Patients with sickle-cell disease have a compensated anaemia (usually 60–80 g/L) with a reticulocytosis and sickle cells on the blood film. Hb electrophoresis demonstrates a predominance of HbS with absent HbA.

Provoke Factors For Sickle Cell Crisis

Experts don’t fully understand the reasons behind a sickle cell crisis. But they do know that it involves complex interactions between RBCs, endothelium (cells lining the blood vessels), white blood cells, and platelets. These crises usually occur spontaneously.

Sickling may be triggered by conditions associated with low oxygen levels, increased blood acidity, or low blood volume.

Common sickle cell crisis triggers include:

• sudden change in temperature, which can make the blood vessels narrow
• very strenuous or excessive exercise, due to shortage of oxygen
• dehydration, due to low blood volume
• infections
• stress
• high altitudes, due to low oxygen concentrations in the air
• alcohol
• smoking
• pregnancy
• other medical conditions, such as diabetes

It’s not always possible to know exactly what caused a particular sickle cell crisis. Many times, there’s more than one cause.

Management

Patients with sickle disease should receive prophylaxis with folic acid. Pneumococcal infection may be lethal in the presence of hyposplenism; patients should therefore receive prophylaxis with daily penicillin V and vaccination against pneumococcus. Patients should also be vaccinated against Haemophilus influenzae B and hepa- titis B.

Vaso-occlusive crises are managed by aggressive rehydration, oxygen therapy and adequate analgesia (which often requires opiates) and antibiotics. Top-up transfusion may be used in seques- tration or aplastic crises. Exchange transfusion, where a patient is simultaneously venesected and transfused to replace HbS with HbA, may be used in life-threatening crises. The oral cytotoxic agent hydroxycarbamide(also known as hydroxyurea ) induces increased synthesis of fetal Hb (HbF- α2γ2), which in turn inhibits polymerisation of HbS and reduces sickling; this may be helpful in individuals with recurrent severe crises. Allogenic stem cell transplantation (also called allogenic bone marrow transplantation) is rarely performed but may be potentially curative it works by using healthy blood steam cells from a donor to replace diseased or damaged bone marrow of the patient. Sickle-cell anaemia has mortality of 15% by the age of 20 yrs and 50% by the age of 40 yrs.

Conclusion

Stem cell or bone marrow transplant seems to be only cure for sickle cell disease but not done for all patients,common treatments might include medications and blood transfusion, keeping the patient hydrated is very important to maintain blood volume at adequate level to prevent sickling.there are some known triggers that can provoke sickle cell crisis but in many times it’s not clear what exactly caused a particular sickle cell crisis, what is clear is that these crisis happen due to interactions between blood cells (especially red blood cells) and lining of blood vessels.signs and Symptoms mostly appear in early months of life. A blood film can show sickled red blood cells that formed after distortion of the membrane due to polymerization of HbS molecules that causes various signs and symptoms like vaso-occlusive crisis, sickle chest syndromes,and some others whilst the second is the most common cause of death among adult ages.carriers of HbS gene show to have some kind of resistance against severe forms of malaria at the same time this disease is prevalent in districts that malaria is endemic.although SCD affects millions of people around the world but Africa has the highest percentage of afflicted people.A point mutation in beta chain of hemoglobin causes replacement of glutamic acid by valine followed by changes in the structure and functions of hemoglobin which leads to sickling of red blood cells resulting in sickle cell anemia(among sickle hemoglobin-c disease and sickle beta-thalasemia)is the most common type of sickle cell syndromes and inherited recessively on chromosome 11.sickle cell syndromes are hereditary hemoglobinopathies which include disorders of hemoglobin. Normal hemoglobin has two states(Tense state>when deoxygenated and Relaxed state>oxygenated) comprise two identical alpha chains and two identical non-alpha chains that together known as globin with a heme group>a metal complex with iron that can bind or release molecular oxygyn O₂ or CO₂ molecules reversibly O₂ from lungs to tissues,CO₂ from tissues to lung and then pushing it out during exhaling.there are no incurable diseases only lack of will ,are we willing ?!

Sickle cell anemia is severe, chronic and even fatal disease. It causes red blood cells to break down and and sickle (form a crescent shape). It occurs due to a point mutation in the Red blood cells which blocks blood flow therefore there is a chronic deprivation of oxygen which leads to complications such as damage to nerves, kidneys, liver, spleen and other organs in the body. Therefore it is important to find a cure, Gene therapy is one of the experimental techniques being researched to treat sickle cell anemia. It involves various genetic technologies that either cure sickle cell disease or make it milder which reduces symptoms and prevents complications. For example, technologies such as zinc finger nuclease are used to snip out the defective gene (HBS) and add in the correct one and lentiglobin gene therapy which introduces a functioning version of the HBB gene into the patients hematopoietic stem cells via a viral vector. These technologies treat sickle cell anemia as they remove the defective genes and replace them with correct functioning ones allowing them to live without complications which improves their quality of life.

About the genetic disease

Name- Sickle Cell Anemia

Cause- It is caused by a mutation in the gene in which forms abnormal haemoglobin (haemoglobin S) that causes red blood cells to become rigid, sticky and misshapen. This sickle cell gene is inherited and passed on through each generation through autosomal recessive inheritance patterns (rr). This means for the child to inherit the disease both parents must be a carrier and pass on the sickle cell gene. However if only one parent passes on the sickle cell gene this child will be a carrier meaning he/she will contain both normal and sickle cell haemoglobin.

Symptoms

• Fatigue and anemia- This occurs due to low oxygen levels in the body
• Swelling and inflammation of the hand or feet
• Arthritis
• Pain crises in the joints and can be sudden in the chest.
• Hematuria or blood in urine.
• Delayed development
• Pallor or yellow skin and eyes
• Shortness of breath.
• Acute Chest syndrome
• Recurring bacterial infections.
• Sudden pooling of blood in the spleen and liver congestion.
• Lung and heart injury.
• Leg ulcers.
• Death of portions of bone
• Eye damage

Age of onset

Sickle cell anemia is usually diagnosed at birth. However, the age of onset can range from 2 months to 176 months. The symptoms of the disease are often prevalent from 4 months of age.

Incidence

Around 70,000 to 100,000 Americans have sickle cell anemia as it is one of the most common inherited blood disorders in the USA. It is most common in ethnic groups such as African americans and hispanics.

Estimates of SCA:

• SCD occurs among about 1 out of every 365 Black or African-American births.
• SCD occurs among about 1 out of every 16,300 Hispanic-American births.
• About 1 in 13 Black or African-American babies is born with sickle cell trait (SCT).
• Survival to adulthood for children with SCD is predicted to be 99 percent in London, 97 percent in Paris, and 94 percent in the U.S.

Prevalence

Sickle cell anemia is most prevalent in areas where outbreaks of malaria occur or have occurred in the past. This is mostly in Africa or in those who have ancestors from Sub saharan Africa, indian, Saudi Arabia and Mediterranean countries.This distribution has occurred due to the spread of malaria in the past which was very common in these countries. As a result the sickle cell trait obtains a survival advantage against malaria and that the selection pressures caused by malaria has resulted in more occurrences of the sickle cell allele. Due to human migration over the years individuals obtaining the sickle cell allele carried it with them all over the world.

The global birth prevalence of the disease is 0.11% but it fluctuates from country to country 5% of the world’s population are carriers of the disease However it is most prevalent in Africa. There are more than over 200,000 cases of SCD in Africa

The prevalence of the sickle cell trait (Carriers of the disease) is from between 10%-40% across equatorial Africa and decreases to between 1% and 2% on the north African coast and In west African countries such as Ghana and Nigeria, the frequency of the trait is 15% to 30% whereas in Uganda there are tribal variations,as it is 45% among the Baamba tribe.

Range of genes/mutations involved

The haemoglobin beta gene located on chromosome 11 is responsible for sickle cell anemia as it causes a mutation. Haemoglobin A is the normal, healthy haemoglobin gene . The red blood cells that contain this form of haemoglobin are round, smooth and can pass through blood vessels. However individuals that have sickle cell anemia obtain the haemoglobin S which consists of abnormal haemoglobin molecules that stick to each other and form a curved red blood cells which causes them to become stiff and rigid forming a sickle shape. The red blood cells then pile up which causes blockages and damages vital organs and tissues.

Sickle cell anemia is caused by a single point mutation, where a single nucleotide base is changed, added or removed from a sequence of DNA or RNA in the corresponding position on the complementary strand. The point mutation occurs in the b-Globin chain (beta globin) of haemoglobin which leads to the hydrophilic glutamic acid being replaced with the hydrophobic amino acid valine at the sixth position.This occurs as the HBB gene( the gene that codes for beta globin) is replaced with its variant HBS which produces sickle cell disease. The resulting protein still obtains 147 amino acids however due to the single nucleotide change the normal haemoglobin gene is transformed into a sickle cell one.Therefore the sequence for the Mutant haemoglobin contains the code GTG instead of GAG.

What is known about the protein product of the gene(s) involved?

The protein product of the HBB gene is a protein called Beta Globin. This is a small part of the larger protein Haemoglobin which is made up of the beta globin and alpha globin (HBA) subunits. These are responsible for carrying oxygen around the body . Mutations in the HBB produce different variations of the proteins which correspond with diseases such as sickle cell anemia.

For a normal haemoglobin molecule. One HBB gene and one HBA1 gene combine to form a dimer and then 2 dimers combine to form the 4 chain tetramer which is the haemoglobin A molecule. However, for sickle cell anemia HBS, A HBB variant is produced by a point mutation in which the codon GAG is replaced by GTG. HBS replaces both beta globin subunits in haemoglobin, or it can replace one and the other beta globin would be replaced with sickle-hemoglobin C (HbSC) or S-beta thalassemia (HbSBetaThal) which are all variations of sickle cell disease.

This occurs due to the hydrophobic valine which has replaced the hydrophilic glutamic acid. The hydrophobic valine will be located on the outside of the haemoglobin protein facing the water even though it is hydrophobic. Due to the hydrophobicity of the valine when 2 or more valines interact they will stick to one another shielding themselves from the cytoplasm. As the hydrophobic valines from different haemoglobin proteins adhere to one another, long chains begin to form within the red blood cells . This is what causes the sickling of the red blood cells.

How genotype contributes to disease phenotype (i.e. how do changes to the protein result in the symptoms)? There are different genotypes for sickle cell anemia individuals with the genotype AS obtain the sickle cell trait phenotype whereas individuals with the SS genotype obtain the sickle cell disease phenotype. The genotype of the individual is what contributes to disease phenotype. The changes in the protein (haemoglobin A) result in the red blood cells to form a sickle cell shape. Due to the abnormal shape of the blood cells they get stuck in blood vessels which cause complications as they slow/block blood flow to parts of the body. These sickle shaped cells also can die prematurely , leading to anemia. As blood flow is blocked and inadequate oxygen is circulated around the body it causes pain, high BP in lungs, stroke, pulmonary hypertension, organ damage, blindness, gallstones and many other complications.

Inheritance patterns

Sickle cell anemia has autosomal recessive inheritance patterns. This means that both parents are a carrier of the sickle cell trait. However they usually do not show symptoms of the disease. The offspring will inherit 2 mutated genes, one from each parent. When two parents who are carriers of the sickle cell disease produce offspring, the chance that the offspring will inherit the disease is evident in fig 1 and fig 2. This is the most common inheritance patterns which are highly prevalent in Africa.

In the following punnett squares both parents are carriers of the sickle cell allele and it is evident that the offspring produced would have a 25% chance of inheriting sickle cell disease, a 50% chance they will be a carrier of the disease like their parents and and a 25% chance that they will not inherit the disease.

Current methods of diagnosis and treatment

There are many methods of diagnosis and treatment for sickle cell anemia for example :

A blood test can test for Haemoglobin S in which a blood sample is taken from a vein in the arm, in younger children it is taken from the finger or heel. This is then transferred to a laboratory where it will be screened for Haemoglobin S. If the test results are negative, this indicates that there is no sickle cell gene present, however if it is positive then more tests will be conducted to identify if one or two sickle cell genes are present. If the test is positive it is not always the case that the individual has sickle cell disease they may only have sickle cell trait therefore additional testing needs to be conducted to gain a definite diagnosis.

Further testing is also necessary for those diagnosed with sickle cell anemia this includes more blood tests and urine tests to monitor the patient for kidney problems or infections. Doctors may also suggest a transcranial doppler ultrasound screening (TCD). This is a procedure which applies sound waves to observe blood flow in the brain. It is used to detect the probability of a stroke and ensure the patient is receiving treatment when required.

In babies sickle cell disease is usually diagnosed by sampling some of the fluid around the baby inside the mother’s womb(amniotic fluid) to detect sickle cell gene Gel electrophoresis can be conducted to determine whether the child has inherited sickle cell disease or trait from both parents this is done through DNA profiling.

Treatment

A common method of treatment is bone marrow transplant. This transplant is usually for patients under the age of 16. First the patient is treated with chemotherapy to get rid of the unhealthy bone marrow. Then via a donor (their siblings) the patient will receive healthy bone marrow which is transferred to them through a vein. This is the only known cure for sickle cell disease.

Doctors also recommend common medicines to treat sickle cell anemia such as antibiotics such as penicillin which prevents infections, pain relieving medicines and Hydroxyurea which reduces the frequency of painful crises and decreases the need for blood transfusions. It works by stimulating the production of fetal haemoglobin- a form of haemoglobin prevalent in newborns that prevents the formation of sickle cells

Hydroxyurea seems to work by stimulating production of fetal hemoglobin — a type of hemoglobin found in newborns that helps prevent the formation of sickle cells making sickle cell disease milder.

Gene therapy

Gene therapy is an experimental technique in which healthy, normal genes (structures of DNA) are introduced to a patient to treat their genetic disease. The healthy genes replace defective or missing genes within the cell. Gene therapy is used to treat sickle cell anemia by altering the patient’s hemoglobin genes or introducing a healthy copy of the mutated gene to the body.

One of the strategies applied for gene therapy is bone marrow transplant, bone marrow transplant applies a combination of gene therapy and chemotherapy to treat sickle cell anemia. This process involves altering the patient’s hematopoietic stem cells. Before undergoing the transplant patients, undergo chemotherapy to eliminate their existing bone marrow. For the process to proceed the patient must have a donor with matched DNA this is usually siblings or someone with the same bone marrow type. The patient’s own bone marrow is taken then the defective stem cells are isolated. In the laboratory the normal healthy gene is inserted into these stem cells to prevent them from sickling then the bone marrow cells are then transferred back to the patient.

Other techniques are also being experimented on such as zinc finger nuclease and lentiglobin.

Zinc finger nuclease

zinc finger nucleases (ZFNs), are proteins specifically designed to grab onto a sequence of DNA and cut it, snip out one version of a gene and then another technique is used to replace it with the correct one. These work by binding to the DNA at a specific targeted sequence and creating a double strand break. These can effectively mutate or eliminate genes of interest . For example, ZFN can target disruption of the BC11A gene, this gene is responsible for turning off the production of fetal haemoglobin. If the BC11A gene is turned off the production of fetal haemoglobin resumes. This prevents the sickling of the blood cells therefore making sickle cell disease milder.

Lentiglobin

Lentiglobin is a viral vector construct which contains the normal gene for haemoglobin.The healthy version of the B_globin gene is inserted into the patients blood stem cells. This produces normal red blood cells instead of sickle cell ones.

A functioning copy of the haemoglobin gene, this is packaged into a lentiviral vector, this contains the HIV virus (human immunodeficiency virus) which is highly effective at inserting genes into cells (the vector has been modified so it cannot pass on hiv infection).

First the patient’s own healthy stem cells are collected from their bone marrow.

The lentiviral vector will then be inserted into the patients stem cells (outside the body) this contains the functioning copy of the haemoglobin gene . The corrected gene will be inserted back into the Dna of the patient. Which will produce a modified stem blood cell which will grow and produce new blood cells containing normal haemoglobin. During this process chemotherapy is applied to remove defective stem cells.

Risk/Benefit Analysis of inquiry question

Benefit

As research on gene therapy techniques increases, gene therapy can be applied in the future to act as a cure for sickle cell anemia this will increase survival rates and prevent complications.

If gene therapy is applied:

The Quality of life will improve for those suffering with sickle cell anemia, this is a benefit as it can prevent complications that arise from sickle cell anemia and can completely eliminate the disease.

The effects will be long lasting and will ensure future generations do not inherit the disease. When the defective genes are removed these will not transfer to the offspring of the following generation.

It will not require a correct match of DNA as there are technologies such as ZFN that exist whereas for processes such as bone Marrow transplant a correct match of DNA is required for the patient to be cured.

A new field of medicine can be created this is a benefit as gene therapy can be used to not only treat sickle cell anemia but many other diseases that occur due to defects in genes such as cystic fibrosis, cancer, heart disease etc..

Risks

Immune response-As a result of a viral vector being introduced to the body, the immune system fights off bacteria and viruses and may do so for the viral vector. This results in inflammation and can cause serious illnesses and even death. This has occurred in many cases for example, in 1999 Jesse Gelsinger had a rare liver disorder, he undertook gene therapy to overcome it however he died due to complications of an unwanted inflammatory response due to the viral vector being introduced to his body .

Targeting the wrong cells.- In order for gene therapy to work successfully the introduced gene must integrate itself into the patients DNA. However it can sometimes integrate itself at a different location infecting another gene. This causes healthy cells to be damaged and can lead to other diseases such as cancer and leukemia.

There is always the risk that when the virus is used to deliver the gene into the patient’s body that it can integrate into the patient’s reproductive cells. This can cause significant changes that can be passed on to the patient’s offspring.

Comparison with prior methods of treatment

The prior and current methods of treatment for sickle cell anemia include antibiotics, pain relieving medications, hydroxyurea and bone marrow transplant these are the most common methods of treatment that have been used to this day. However as technology advances, there have been many experimental techniques such as gene therapy and genetic editing.

“This disease has impacted my life in so many different ways: good and bad.” These are the words from Natasha Thomas, a woman who was diagnosed with sickle cell disease at the age of seven. Sickle cell disease is a blood disorder that affects the red blood cells in the body. A healthy red blood cell is normally round and the sickle cells are half-moon shaped. This irregular shape does not carry enough oxygen throughout the body causing organ damage and when these half shaped cells cluster together, they can cause severe pain.

Sickle cell results from a mutation in a certain hemoglobin gene found on chromosome 11. The normal codon for someone who doesn’t have this disease is GAG but for a person who has sickle cell, the ending codon would be GUG. This causes there to be a different amino acid, valine instead of glutamine which causes the condition. Sickle cell disease is autosomal recessive which means two copies result in the sickle cell trait. To get this, you would have needed to inherit one gene from your mother and father. Natasha did not say her parents had this disease, but we can assume that her parents both had it or were both carriers since Natasha and her brother were both diagnosed. Natasha is from African descent and she said that it is most common in their race but it is quite misunderstood that only African descent is affected.

Having this disease, you don’t have many noticeable physical features unless you have the symptom of Dactylitis, which is having swollen hands or feet. It does have physiological effects like organ damage to the heart, gallbladder, eyes, liver, bones, and joints. It is very limiting in physical activities because it can cause a large amount of physical distress, even causing some active people to collapse or even die during exercise and playing sports. Natasha said at a younger age, due to sickle cell, she had to drop out of her dance group which she loved very much and now running is very difficult for her.

To see if you have this disease, you are tested by a blood test, which is how Natasha found out at seven years old, which is an older age to have been diagnosed. Most people are diagnosed at birth or around four months when symptoms begin to show significantly. Doctors try to do a blood test as soon as possible so the proper treatments can be given to the baby, although, there is not any way to prevent or cure this. There are a variety of treatments available to help with some symptoms associated with sickle cell disease. One treatment option is chronic blood transfusions which Natasha had only needed once in her life. A chronic blood transfusion is used to increase tissue delivery of oxygen and to provide normal red blood cells to the body. Another form of treatment is Hydroxyurea and it is a drug used to decrease painful episodes. When it’s put into the body, it makes the red blood cells a larger shape and keeps them flexible so it is not as likely to turn into a sickle shape. Natasha does not qualify for this drug because you need to have been hospitalized four times a year. There is a new drug that just got FDA approved and Natasha may finally qualify for it and it is called Oxbryta. The making of this drug is a huge milestone and breakthrough for those suffering from this condition because it helps treat the root cause of sickle cell disease.

At St. Jude and many other places, there have been a few clinical trials done to help find a cure for sickle cell disease. Out of these trials, the one that seems the most effective and successful is gene therapy, which is given to many with this condition to help them a great amount. Gene therapy is allowing doctors to alter and reverse some of the patient’s stem cells which is meant to repopulate the bone marrow to make healthy blood cells in the body. In another clinical trial for gene therapy, they are trying to replace the mutated gene with a healthy gene in hopes of reducing the sickle-shaped cells and help with the pain. Many doctors and hematologists believe that one day they will be able to hopefully find an ending cure to sickle cell.

With all these clinical trials and therapies going on, it can get quite expensive and funding for this isn’t at its best. Over time, costs for this disease have gone higher than $1 billion in research, new treatments, and many other things dedicated to improving the lives of patients. One of the biggest contributions with funding to sickle cell is when the Legislation of Congress signed a bill to give $4 million to help with treatments. Many patients with this condition believe they deserve better funding because costs do build up over time. Some people who qualify for different drugs to help aren’t told about them or given the chance to take them. Dr. Sophie Lanzkron, who directs the adult sickle cell clinic at Johns Hopkins Medicine, says “We should be prescribing it to everybody who’s eligible, and everyone who’s eligible should be taking it.” Natasha also believes that funding should be better because her brother, who I mentioned before, died from this condition at the age of 25. Natasha does not want her family to go through the same thing if anything was to happen to her. Sickle cell affects many people worldwide but yet so many people don’t know much about it. More awareness should be made about people’s lives who have sickle cell, including Natasha Thomas.

Abstract

Sickle cell anemia (SCA) is a globally prevalent, monogenic, life-threatening blood disorder with a complex pathology that remains obscure. A deepened understanding of the malady in the recent years has led to pharmaceutical advancements that target pathophysiology and ultimately ameliorate associated multivariate clinical manifestations. Abnormal cell to cell interactions, endothelial adhesion, induced oxidative stress, intracellular erythrocyte dehydration and concentration levels of fetal hemoglobin are a few factors know to play a key role in microvascular obstruction in individuals with Hemoglobin S. All of which have recently been manipulated in vitro to pharmaceutically alter clinical complications, disease progression and mortality patterns.

The purpose of this paper is to provide a condensed overview of recent discoveries made within SCA pathology and subsequent pathologic based therapeutic agents. A general overview of the molecular basis of the malady, global prevalence and the efforts toward advancing stem cell transplantation technology will also be discussed.

Introduction

Sickle cell disease (SCD) denotes a group of pleiotropic hemoglobinopathies that mechanically affect the body’s vasculature. Of the various forms, Sickle Cell Anemia or homozygous Hemoglobin S (HbS) is the most common. It is characterized by the production of abnormally shaped red blood cells, which can obstruct and damage circulation; initiating a cascade of atypical cell interactions. Decreased organ perfusion to the kidneys, spleen, nervous, cardiovascular, respiratory and urinary systems become imminent in the absence of appropriate pathophysiology specific therapy (Lanzkron, Carroll, & Haywood, 2010). Sickle cell crisis is the most prevalent clinical complication associated with SCA and usually precedes multivariate symptoms correlating with decreased organ perfusion and functioning.

There are 100 million carriers of heterozygous Hemoglobin AS or sickle cell trait (SCT) worldwide. Global prevalence suggests a long standing selective pressure against falciparum malaria and consecutive carrier migration from malaria endemic regions(Gong et al., 2012). SCT carriers demonstrate minimal, if any clinical complications throughout one’s lifetime.

Nevertheless, 300,000 babies are born to these carriers each year with a 25% chance of their children inheriting SCD. The benefits of SCT genotyping and fetal screening has directly impacted mortality and morbidity patterns in resource accessible regions. Limited access to frontline therapies and proper medical follow in malaria endemic and developing regions are great attributors to disease prevalence. Moreover, a deepened understanding of the complex pathology of SCA in the past decade has encouraged researchers to shy away from panoptic therapies and gear toward development of pathology modifying interventions that ultimately decline global incidences on a greater scale.

Inheritance of the sickle cell gene causes a non-conservative missense mutation at the beta globin chain(Manwani & Frenette, 2019). The exchange of hydrophobic valine with hydrophilic glutamic acid on the 6th position of beta globin induces hemoglobin S to sickle in anoxic and acidic microenvironments; also referred to as the deoxy-sickle hemoglobin phase. Mechanical obstruction of the micro-vessels by recurring red cell sickling has been tipically estimated as the sole reason for decreased organ perfusion and tissue infarction; yet recent scientific progress proves otherwise. Further demystification of the mechanistic complexity of HbS has led to pharmaceutical advancements aimed to target abnormal endothelial interactions, inflammation and red cell dehydration in individuals with the life compromising disease.

Manipulation of vasoactive factors in vitro has demonstrated encouraging results for new oral therapeutic agents anticipated to impact individuals in developing regions. Frontline SCD therapies such as hydroxyurea and blood transfusions vary in clinical efficacy from patient to patient and is not readily accessible in impoverished regions. Stem cell transplantation is the only curable option for SCD yet advancements in donor transplantation and remain limited. Although a thorough investigation of the complex, multivariate pathophysiology of SCD does not fall within the scope of this review, emphasis will be placed on disease targeting agents that are being studied to date that perpetuate a less hindering clinical outcome in those suffering from SCA.

Increasing fetal hemoglobin concentration

Increased levels of fetal hemoglobin (HbF) has long been understood to improve SCA related clinical complications. Having 2 alpha and 2 gamma chain tetramers physiologically inhibits HbF from entering the deoxy-sickle hemoglobin phase. Contrary to adult hemoglobin, fetal hemoglobin decreases the likelihood of HbS polymerization. During gestation, fetal hemoglobin predominates until its regression to less than 1% at nearly 6 to 12 months after birth. This phenomenon accounts for why most SCD infants are asymptomatic in the first few months. Moreover, baseline fetal hemoglobin concentrations fluctuate amongst haplotypes of the sickle cell gene. Senegal and Saudi-Indian haplotypes manifest higher HbF levels in adulthood and thus demonstrate a milder clinical expression contrary to the other beta S-globin haplotypes. Pharmacologically inducing fetal hemoglobin levels strongly correlates with a reduction in episodes of pain crises, hemolysis and longer survival.

For over 30 years, Hydroxyurea (HU) remains the therapeutic standard for modifying SCD pathogenesis and increasing HbF. HU is mechanistically known to inhibit the formation of deoxyribonucleotides, thereby trapping cells in the synthesis stage of the cell cycle and stimulating erythropoiesis. Consequentially, the intercalation of fetal and adult hemoglobin (HbA) hinders the polymerization of HbS and subsequent red cell sickling. HU related studies have also proved that clinical efficacy is not only a result of HbF production but also a demotion of abnormal blood cell interactions, endothelial adherence, blood viscosity and premature intravascular hemolysis. The Multi-Center Study of Hydroxyurea (MSH) was a prominent placebo controlled randomized trial for adults in 1999 that revealed a 44% reduction in pain crisis in the placebo group. Furthermore, fewer episodes of acute chest syndrome, splenic sequestration, transfusion induced hospitalizations and priapism were also reported. In 2011, HU was considered by the Food and Drug Administration to be an appropriate therapy for children over 2 years old. The BABY HUG study was the first placebo-controlled randomized trial of HU in adolescents that even included infants with mild clinical complications. Of note, the placebo group demonstrated a 5 times higher dactylitis occurrence and 3 times higher incidence of acute chest syndrome.

Hydroxyurea for children is arguably underused in malarial-endemic regions where the greatest sickle cell burden prevails(Diallo & Tchernia, 2002). The NOHARM, placebo controlled multicenter study was one of the first of its kind to test the efficacy of HU on children in malaria-endemic Uganda. HU recipients had demonstrated benefits similar to trials performed in non-malarious regions; including a less frequent SCA-related clinical outcome, a notable decrease in reticulocyte formation, splenic sequestration and the need for blood transfusion compared to the placebo group. Despite the encouraging results, the demand for optimal HU dosing and proper regimen monitoring remains a challenge. With the maximum dosage being 35mg/kg in order to avoid cytopenia and toxicity, HbF induction via hydroxyurea is considered lower than the magnitude expected to completely prevent SCA related clinical complications. In fact, studies have proven that HbF induction via Hydroxyurea varies amongst individuals with reports of baseline regression status post 2 years of treatment. Moreover, rates of non-adherence to HU secondary to an unvaried treatment outcome is also a contributor of the delayed decline in disease prevalence. Thus, the need for a robust HbF inducing agent is imminent in effectively treating mortality rates in heath-impoverished regions.

Pharmacological advancements in HbF biochemistry resulted in the genetic manipulation of HbF gene silencer, DNMT1. 5-aza-2’-deoxycytidine (decitabine) functions to bind and deplete DNMT1 and therefore upregulate fetal hemoglobin in erythrocytes. The first human study on the efficacy of decitabine in HbF induction was performed in 2017 and demonstrated an encouraging outcome for larger trials forthcoming. The randomized trial administered decitabine with the oral multidrug resistant transporter, tetrahydrouridine (THU) in order to expand bioavailability and counteract pharmacologic limitations. The randomized, phase I/II study revealed an increase in fetal hemoglobin levels to 80% of total erythrocytes in the treated group. A decline in levels of cellular adhesion and reticulocyte production were also noted. Although Decitabine has potential toxicities as does HU, this HbF inducer demonstrates a greater efficacy even in patients non-responsive to Hydroxyurea. While the demand for more research remains, oral interventions that genetically manipulate the HbF gene may allow less follow-up need in regions that may not have access.

Sickle Cell Anaemia is an autosomal recessive disorder which is passed through generations; meaning it is a hereditary disease. To inherit Sickle Cell Anaemia an individual must receive a mutated gene from both their paternal and maternal side. Those who only receive one mutated gene are said to be carriers of the disease but are not affected.

Sickle Cell Anaemia is most commonly found in Mediterranean countries which have African descent. According to (Hematology.org, 2019) Sickle Cell Anaemia affects 1 million to 3 million Americans and 8 to 10 percent of African Americans. Meaning that more than 100 million people worldwide are currently living with Sickle Cell Anaemia.

Sickle Cell Anaemia is caused by a mutation in the HBB gene also known as haemoglobin beta which is found on chromosome eleven, this codes for production of haemoglobin for red blood cells. The type of mutation that occurs is called a point mutation, this happens when a base sequence in the coding DNA has a base changed in its nucleotide sequence. The nucleotide base sequence which codes for the gene haemoglobin beta (HBB) is; GAG also known as guanine, adenine and guanine. However, the nucleotide base sequence in individuals with Sickle Cell Anaemia for haemoglobin is; GTG also known as guanine, thymine and guanine. These errors occur in the transcription stage of protein synthesis where the information from genes are taken and transcribed onto messenger RNA (mRNA) to be further transcribed at a later point in the process.

One the point mutation has taken place and the nucleotide sequence has been transcribed onto messenger RNA (mRNA), it is taken to the ribosomes in the cytoplasm of the cell where it can be translated into an amino acid. The transfer RNA (tRNA) carry the anticodon which is responsible for matching the correct complementary base sequence to the codon base sequence of nucleotides on the mRNA. Each anticodon is specific to one type of amino acid. This means that the bases on the mRNA strand is read in coding triplets, because every three bases codes for an amino acid. In saying this when the point mutation GTG; guanine, thymine and guanine was read by the tRNA it will have been given the anticodon CAC; cytosine, adenine and cytosine. This means that the amino acid produced is Valine rather than the Glutamic acid which is produced in the normal process of making haemoglobin. This mutated form of haemoglobin found in individuals with Sickle Cell Anaemia is called HbS. This change in protein sequence causes a change in structure of the haemoglobin causing the biconcave shape of the red blood cell to be disformed. This deformity is in the shape of a crescent.

The mutated amino acid Valine is positioned on the top of the protein structure meaning that once it loses oxygen there is a hydrophobic region on the Valine amino acid which can then react with large fibres of granular haemoglobin. This is what causes the distorted crescent shape of the red blood cells in Sickle Cell Anaemia. This crescent shape causes many disruptions in the function of the red blood cell as the biconcave shape is used for its large surface area to carry oxygen from the lungs to cells and carry carbon dioxide away from cells back to the lungs as a waste product. This sickle crescent shape decreases the surface area meaning less area for oxygen to diffuse out of the red blood cell into the body and less area to pick up waste carbon dioxide from the cells. This in turn can cause fatigue and weakness making daily tasks with this disease more challenging.

The crescent shape of the red blood cell is fragile meaning they often rupture and cannot serve their purpose. Also due to the extra fibres attached the red blood cells are less flexible and often get caught in the capillaries and cannot pass through causing blockages which slow down or stop the flow of red blood cells in that area. This can cause damage to organs and tissue due to a lack of oxygen which would have been carried on the red blood cell. Individuals may also suffer from swelling of the legs and arms due to blockages in the capillaries which can be painful.

There is currently only one potential cure for Sickle Cell Anaemia; bone marrow transplant which is also known as stem cell transplant. This procedure requires the individual to find a donor of the same type of stem cells so that the transplant will be successful. Once a donor has been found stem cells can be extracted from the donor usually from the hipbone. This is then harvested into the patient with Sickle Cell Anaemia. Stem cells are undifferentiated cells meaning that they have the potential to change form and function depending on their location of origin. In successful cases the stem cells can correct the mutated gene for HBB and give fully functioning red blood cells. This treatment can be a very lengthy process in trying to find a matching donor, alongside its adverse side effects. Therefore, it is not used as a method of treatment in those under the age of sixteen years old.

There are other methods of treatment, although they are not cures, they help to reduce the severity of the symptoms for example, young children may take antibiotics to help resist against illnesses such as pneumonia which otherwise could be fatal to a young child with Sickle Cell Anaemia.

As suggested by Sickle Cell patients may also receive Hydroxyurea which is take orally daily to help to increase the number of haemoglobin in the body and reduce the need for blood transplants. However, studies have shown that this drug can increase the individual’s risk of infection and so long-term use can cause issues later in life. In saying this blood transfusions could be a more reliable source of treatment as it has less possibility of adverse health conditions, although the demand for blood could make this treatment less readily available.

Currently there is prospect of gene therapy being used to treat Sickle Cell Anaemia. Gene therapy is when individual’s defected genes are targeted and genetically engineered to produce a functioning gene by adding a functioning copy of the gene required. There are currently two strategies which both involve altering the individuals hemopoietic stem cells. As stated by these are stem cells found in the bone marrow which divide and specialise to produce different types of blood cells.

The first of the two strategies involves extracting the patients hemopoietic stem cells and replace the mutated HBB gene in these cells and replace it with the fully functioning gene for haemoglobin. One this is completed the stem cells would be harvested back into the patient using an inactive virus with hope that the steam cells would divide and differentiate with the ability to produce haemoglobin rather than the mutated version.

The second strategy involves genetically altering a different gene in the patients hemopoietic stem cells to enhance the production of foetal haemoglobin. This is produced by babies 3 months after conception until around 6 months old. This type of haemoglobin represses the production of sickling or ‘crescent shaped’ cells in patients with Sickle Cell Anaemia. However, people only produce very little amounts of these after infancy. The aim of this strategy is to increase production of foetal haemoglobin by using an enzyme to cut the section of DNA which supresses the production of foetal haemoglobin. This should then allow the cell to produce more foetal haemoglobin.

What is sickle-cell anaemia

Sickle-cell anaemia is a hereditary, homozygous, genetic blood disorder that occurs within a person who has abnormal haemoglobin on their red blood cells. The Haemoglobin are sensitive to low amounts of oxygen in the body which makes them transform into sickle or crescent shapes. This causes the abnormal haemoglobin to become stiff and sticky blocking blood flow to important organs and tissues. Healthy red blood cells will survive within the body for 120 days however, sickle-cells will rupture and break down within 20 days. The spleen is an organ which recycles old red blood cells and fights infection. Sickle-cells cause the spleen to become overwork and blocked, the bone marrow often can not keep up with the frequent lack of red blood cells and this can cause anaemia.

Symptoms of sickle-cell anaemia are usually presented in early childhood. Patients usually show symptoms between six to eight months of age. The symptoms may include pain, fever, swelling of the hands and feet but vary from person to person. Some people may show mild symptoms where others may require frequent hospital visits. This disease affects many people throughout the world mainly those whose ancestors migrated from Africa. A person who is born with the homozygous genotype “SS” will have sickle-cell anaemia.

This image shows carrier parents with genotype Ss. The parents will produces a future generation with a twenty-five percent chance of having sickle-cell anaemia genotype SS, twenty-five percent chance of not having sickle-cell anaemia genotype ss and a fifty percent chance of producing a carrier genotype Ss.

DNA and protein synthesis

DNA is made up of nucleotides, these are broken down into sugar molecules, phosphate molecules and a base. There are four base a nucleotide could have, Thymine, Adenine, Cytosine and Guanine. DNA produces large chains of amino acid in a consistent order depending on the nucleotides gene coding. DNA continuously replicates itself, it unzips part of the ladder and new DNA strands will connect up to form additional DNA strands ensuring the survival of DNA for many years. Nucleotides are linked together to make the DNA ladder strand also known as a double helix. Amino acid contains around 20 molecules that are combined to form protein in living organisms.

Darwin’s theory of evolution be natural selection

Darwin’s theory of evolution by natural selection describes variants in plants, animals and fossils. Darwin’s idea challenges the idea God made all that live on earth. His scientific research was published twenty-eight years after he started. Darwin stated, “individuals with characteristics most suited to the environment are more likely to survive and breed successfully, this will allow them to pass on their survival characteristics to the future generations.”

Malaria is a disease carried by mosquitos, when they feed on human blood they pass on a parasite. The single-celled mosquito parasite multiplies in the mosquito’s intestines as well as red blood cells in humans. Areas such as Africa, South Asia and Middle East are at risk of catching the malaria disease. Throughout the generations and following Darwin’s theory of natural selection humans within these areas have evolved in order to survive. Sickle cells anaemia appears more within these countries as a survival trait within the human body. The sickle shape cells die off quicker than the regular red blood cells which causes the parasite carrying the malaria disease to become stuck within them and die along with the sickle shaped red blood cells.

Current piece of research on sickle-cell anaemia

A recent piece of research on sickle-cell anaemia published by Ballas, Samir in June 2002 explains how sickle-cell anaemia influences a person’s life and what steps are taken to relieve pain. Ballas states “…social interactions, intimate relationships, family relations, peer interactions, education, employment, spirituality and religiosity” are all affected when a person is sickle-cell anaemic. There are many different therapies used to manage the disease, a sympathetic approach including pain management, blood transfusion and treatment of organ failure.

Individuals undergoing pain management will be assessed as to what therapy and utilisation period is needed, also an assessment into what medication would benefit the patient will be assessed for adequate pain relief.

Intense chest syndrome is one of the common organ failures amongst the sickle-cell anaemic patients. This syndrome is managed through hostile treatments including but not limited to multiple antibacterials and blood transfusions depending on how severely the patient’s symptoms are. Throughout the last decade there has been significant advances in the way sickle-cell anaemia patients are cared for, one most important aspect was the discovery of hydroxyurea and how this can help patients with sickle-cell anaemia.

In conclusion as humans have two chromosome 11s a person can only have sickle- cell anaemia if both chromosome 11s are affected. If only one chromosome 11 is affected that person will be a carrier of the sickle-cell anaemia disease. Although the disease is more common in areas with malaria as the mutation in the DNA helps fight malaria it can still be found throughout the world.