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Hemoglobin S

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Last Updated: 26 September 2020

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General | Latest Info

Sickle cell disease is a group of disorders that affect hemoglobin, molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disease have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle, or crescent, shape. Signs and symptoms of sickle cell disease usually begin in early childhood. Characteristic features of this disorder include low number of red blood cells, repeat infections, and periodic episodes of pain. The severity of symptoms varies from person to person. Some people have mild symptoms, while others are frequently hospitalized for more serious complications. Signs and symptoms of sickle cell disease are caused by sickling of red blood cells. When red blood cells sickle, they break down prematurely, which can lead to anemia. Anemia can cause shortness of breath, fatigue, and delayed growth and development in children. Rapid breakdown of red blood cells may also cause yellowing of eyes and skin, which are signs of jaundice. Painful episodes can occur when sickled red blood cells, which are stiff and inflexible, get stuck in small blood vessels. These episodes deprive tissues and organs, such as lungs, kidneys, spleen, and brain, of oxygen - rich blood and can lead to organ damage. A particularly serious complication of sickle cell disease is high blood pressure in blood vessels that supply lungs, which can lead to heart failure. Pulmonary hypertension occurs in about 10 percent of adults with sickle cell disease. Sickle cell disease affects millions of people worldwide. It is most common among people whose ancestors come from Africa; Mediterranean countries such as Greece, Turkey, and Italy; Arabian Peninsula; India; and Spanish - speaking regions in South America, Central America, and parts of the Caribbean. Sickle cell disease is the most common inherited blood disorder in the United States, affecting an estimated 100 000 Americans. The disease is estimated to occur in 1 in 500 African Americans and 1 in 1 000 to 1 400 Hispanic Americans. Mutations in HBB gene cause sickle cell disease. The HBB gene provides instructions for making one part of hemoglobin. Hemoglobin consists of four protein subunits, typically, two subunits called alpha - globin and two subunits called beta - globin. The HBB gene provides instructions for making beta - globin. Various versions of beta - globin result from different mutations in the HBB gene. One particular HBB gene mutation produces an abnormal version of beta - globin know as hemoglobin S. Other mutations in the HBB gene lead to additional abnormal versions of beta - globin such as hemoglobin C and hemoglobin E. Hbb gene mutations can also result in unusually low levels of beta - globin; this abnormality is called beta thalassemia. In people with sickle cell disease, at least one of the beta - globin subunits in hemoglobin is replaced with hemoglobin S. In sickle cell anemia, which is the most common form of sickle cell disease, hemoglobin S replaces both beta - globin subunits in hemoglobin. In other types of sickle cell disease, just one beta - globin subunit in hemoglobin is replaced with hemoglobin S.

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Clinical Information

Table

Results SeenConditionGenes
Slightly decreased Hb A; Moderate amount Hb S (about 40%)Sickle cell traitOne gene copy for Hb S ( heterozygous )
Majority Hb S; Increased Hb F (up to 10%); No Hb ASickle cell diseaseTwo gene copies for Hb S ( homozygous )

Homozygous Hemoglobin S is serious chronic hemolytic Anemia most commonly found in those of African or Middle Eastern descent. Hemoglobin S is freely soluble when fully oxygenate; when oxygen is remove, polymerization of abnormal Hemoglobin occurs, forming tactoids that are rigid and deformed cells. This leads to sickling of cells, hemolysis, and many other complications. Heterozygous Hemoglobin S is the most common hemoglobinopathy in the United States. This condition is present in about 8% of African Americans. Usually, Hemoglobin S trait exhibit no clinical or hematological effects. A small fraction of people with Sickle Cell trait have recurrent hematuria.

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Test Overview

Table

Results SeenConditionGenes
Slightly decreased Hb A; Moderate amount Hb S (about 40%)Sickle cell traitOne gene copy for Hb S ( heterozygous )
Majority Hb S; Increased Hb F (up to 10%); No Hb ASickle cell diseaseTwo gene copies for Hb S ( homozygous )

The Hemoglobin electrophoresis test is a blood test done to check different types of hemoglobin in the blood. Hemoglobin is a substance in red blood cells that carry oxygen. Hemoglobin. This is the most common type of hemoglobin found normal in adults. Some diseases, such as severe forms of thalassemia, may cause Hemoglobin levels to be low and Hemoglobin F levels to be high. Hemoglobin F. This type is normally found in fetuses and newborn babies. Hemoglobin F is replaced by Hemoglobin shortly after birth; only very small amounts of Hemoglobin F are made after birth. Some diseases, such as Sickle Cell disease, Anemia, and leukemia, have abnormal types of Hemoglobin and higher amounts of Hemoglobin F. Hemoglobin A2. This is a normal type of hemoglobin found in small amounts in adults. There are more than 350 types of abnormal hemoglobin. Footnote 1 most common is Hemoglobin S. This type of Hemoglobin is present in Sickle Cell disease. Hemoglobin C. This type of Hemoglobin does not carry oxygen well. Hemoglobin E. This type of Hemoglobin is found in people of Southeast Asian descent. Hemoglobin D. This type of Hemoglobin is present in some Sickle Cell disorders. Hemoglobin S and Hemoglobin C are the most common types of abnormal Hemoglobin that may be found by electrophoresis test. Electrophoresis uses electrical current to separate normal and abnormal types of Hemoglobin in the blood. Hemoglobin types have different electrical charges and move at different speeds. Amount of each hemoglobin type in current measure. An abnormal amount of normal hemoglobin or abnormal type of hemoglobin in the blood may mean that disease is present. Abnormal Hemoglobin types may be present without any other symptoms, may cause mild diseases that do not have symptoms, or cause diseases that can be life - threatening. For example, Hemoglobin S is found in Sickle Cell disease, which is a serious abnormality in the blood and causes serious problems.


What is hemoglobin electrophoresis?

Hemoglobin is a protein in your red blood cells that carries oxygen from your lungs to the rest of your body. There are several different types of hemoglobin. Hemoglobin electrophoresis is a test that measures different types of hemoglobin in the blood. It also looks for abnormal types of hemoglobin. Hemoglobin, most common type of Hemoglobin in healthy adults Hemoglobin f, fetal Hemoglobin. This type of hemoglobin is found in unborn babies and newborns. Hgbf is replaced by HgbA shortly after birth. If levels of HgbA or HgbF are too high or too low, it can indicate certain types of anemia. Hemoglobin s. This type of Hemoglobin is found in sickle cell disease. Sickle cell disease is an inherited disorder that causes the body to make stiff, sickle - shape red blood cells. Healthy red blood cells are flexible so they can move easily through blood vessels. Sickle cells can stick to blood vessels, causing severe and chronic pain, infections, and other complications. Hemoglobin c. This type of Hemoglobin does not carry oxygen well. It can cause mild form of anemia. Hemoglobin e. This type of hemoglobin is mostly found in people of Southeast Asian descent. People with HgbE usually have no symptoms or mild symptoms of anemia. The Hemoglobin electrophoresis test applies electric current to blood sample. This separates normal and abnormal types of Hemoglobin. Each type of hemoglobin can then be measured individually. Other names: Hb electrophoresis, Hemoglobin evaluation, hemoglobinopathy evaluation, Hemoglobin fractionation, Hb ELP, sickle cell screen

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Sickle Cell Hemoglobinopathies

Just a single point mutation in the Beta globin gene leads to debilitating damage of Sickle Cell Disease. This inherited change drives complex, unrelenting conditions characterized by vaso - occlusion, chronic Hemolysis, and chronic Anemia. Hemoglobin S polymerization is the root cause of Sickle Cell Disease pathology and its long - term sequelae. In low oxygen environments, Hemoglobin S molecules coalesce and begin to polymerize. Polymers coalesce into long fibers that distort red blood cells into characteristic Sickle shape. Hemoglobin S polymerization is a key event that leads to drastic changes in integrity and function of red blood cells. Polymers deform red blood cell membrane structure, making cells much more rigid and adhesive. This slows or obstructs blood flow, resulting in vaso - occlusion and diminishing oxygen delivery. Lower local oxygen levels induce further sickling, vaso - occlusion, reperfusion injuries, and inflammatory responses. Additionally, membrane changes caused by Hemoglobin S polymers lead to cellular dehydration, chronic Hemolysis, and early cell death. Sickled cells only survive for about 10 - 20 days versus 120 days for healthy red blood cells, which stress bone marrow and increase reticulocyte production. When red blood cells become fragile and lyse, they release hemoglobin and other cellular content that contribute to vasculopathy and further inflammation. Free Hemoglobin is break down, decreasing the amount of active Hemoglobin in circulation and leading to chronic Anemia and its clinical complications. Left unchecked, pathologic effects of vaso - occlusion, chronic Hemolysis, and chronic Anemia can lead to progressive tissue damage and end - organ damage. Organs that may be affected by long - term chronic damage include: brain, eyes, lungs, heart, kidneys, and gallbladder. In summary, single nucleic acid substitution in Beta globin gene causes Hemoglobin S polymerization that initiates extensive pathological changes leading to vaso - occlusion, chronic Hemolysis, and chronic Anemia. There is an ongoing need for improved management of patients with Sickle Cell Disease and related end organ damage.

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Introduction

Observation in slow temperaturejump experiments of delay prior to appearance of polymers was almost simultaneously reported from three different laboratories. In 1974, delay period was observed by Hofrichter et al using birefringence and calorimetry, 37 by Malfa and Steinhardt using viscosity, 38 and by Moffat and Gibson using turbidity. 39 delay is also characteristic of aggregation of peptides and proteins to form amyloid that is responsible for neurodegenerative diseases. The difference between amyloid formation and Hemoglobin S polymerization is that there is small concentration dependence on amyloid formation, while there is enormous concentration dependence on Hemoglobin S polymerization. 37 double nucleation mechanism that could explain both the existence of delay and high concentration dependence was not developed until the work of Ferrone et al. In 1980. This work uses photodissociation of carbon monoxide complex of Hemoglobin S to create deoxyhemoglobin S at any temperature in milliseconds, instead of tens of seconds to minute in earlier slow temperature jump experiments. 40 This method also permits observation of subsecond polymer formation on cells from patients with homozygous SS Disease, which shows that there is little or no difference between deoxyhemoglobin S in purified solutions, and in red cells from patients with disease. 43 double nucleation mechanism also accounts for observation of large fluctuations in delay time in small volumes as result of stochastic formation of first homogenouslynucleated fiber. The 40 41 44 45 experiment is similar in spirit to the first observation of single membrane channel opening and closings in patch clamp experiments, performed just a few years earlier, in which single protein channel kinetics is observed because of zillions of ions that flow when the channel is open to give rise to measurable electrical current. 46 in Sickle Hemoglobin experiment, zillions of fibers formed by heterogeneous nucleation pathway that follows formation of first homogenously nucleated fiber in volume could be detected by light scattering. Mechanism has stood the test of time. 47 Interestingly, double nucleation Hemoglobin S polymerization mechanism is now being used to explain aggregation kinetics of Alzheimer's peptide. 48 49 50 51 52 One of most remarkable predictions of double nucleation mechanism, confirmed by experiment, is that concentration dependence of rate of fiber formation by homogeneous nucleation pathway should be approximately twice the concentration dependence of delay time. Cao and Ferrone find 50 power for the former and 25 power for the latter, 45 for Christoph et al. Find 40 and 80 powers. 53 Even though I would argue that 80 power concentration dependence is one of the most amazing results in the history of chemical kinetics, paper get grand slam. That is, it was rejected without review by Nature, Science, PNAS, and Cell.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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Hemoglobinopathy S

Table

Results SeenConditionGenes
Slightly decreased Hb A Moderate amount Hb S (about 40%)Sickle cell traitOne gene copy for Hb S (heterozygous)
Majority Hb S Increased Hb F (up to 10%) No Hb ASickle cell diseaseTwo gene copies for Hb S (homozygous)
Majority Hb C No Hb AHemoglobin C diseaseTwo gene copies for Hb C (homozygous)
Majority Hb A Some Hb HHemoglobin H disease (alpha thalassemia)Three out of four alpha genes are mutated (deleted)
Majority Hb F Little or no Hb ABeta thalassemia majorBoth beta genes are mutated
Majority Hb A Slightly Increased Hb A2 (4-8%) Hb F may be slightly increasedBeta thalassemia minorOne beta gene is mutated, causing slight decrease in beta globin chain

Sickle cells are some of the most readily identifiable abnormal red blood cells that may be encountered on manual differential and observation of them will assist in positive identification of Hemoglobin S disorder. However, they are not present in all Hemoglobin S disorders, or may not be present in all stages of disorder. This course will update you on laboratory testing that is currently being used to diagnose and differentiate between various forms of Hemoglobin S disorders. You will also learn about clinical symptoms that are associated with each one. The course concludes with several case studies that will provide you with an opportunity to apply what you learn in the course.

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Pathogenesis

Hemoglobin S results from inherited substitution of valine for glutamic acid AS, sixth amino acid of the Beta globin chain. This change produces profound alterations in stability and solubility of hemoglobin molecule. 4 Hemoglobin S molecules polymerize in hypoxic and acidic environments, imparting Sickle shape to erythrocytes. Sickle erythrocytes show increased adhesion. Interaction of Sickle cells with adhesion Proteins of vascular endothelium initiates inflammatory response, which further increases cellular adhesiveness. Increase adhesion and inflammation decrease blood flow, leading to further sickling. Repeat episodes of decreased blood flow may lead to impaired nourishment of critical structures. Vascular occlusion is responsible for bone and joint manifestations of Sickle Cell Disease, including avascular necrosis and increased risk for infection. Synovial biopsy specimens generally reveal microvascular thrombosis, with occasional intraluminal sickled cells, perivascular fibrosis, and mononuclear inflammatory cell infiltration.

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Haemoglobin S solubility test

An 18 - year - old National Collegiate Athletic Association soccer player is being tested for the Sickle Cell trait as a condition for participation. His Sickle Solubility Test is negative. After college, he is shocked when his newborn is diagnosed with Hemoglobin SC disease. His wife is known to have SCT. He present For consultation to understand how his child inherited Sickle Cell disease when his Sickle Test was negative. What are the sensitivities and specificities of screening tests for Hemoglobin S and other variants? Infants with Sickle Cell trait, or other hemoglobin variants, are identified at birth in the US through universal newborn screening for hemoglobinopathies. In contrast to infants with Sickle Cell disease, who are referred for specialty care, approach to those with SCT is not uniform. 1 Parents may not be educated about their infant's screening result and adults may be unaware that they have SCT. 2 There is increased recognition that SCT carries unique health risks, including increased risk of exertional heat - related injuries. 3 This potential for adverse outcomes, along with the fact that adults may not know their trait status, has led some organizations to screen for SCT. The United States Department of Defense and NCAA have released policy statements that address screening tests for SCT. 4 - 6 Reports of EHI - related deaths among military recruits prompted DoD to adopt the policy of universal screening for Hemoglobin S in 1981. In examination of military recruits from this era, risk of sudden death was 27 - fold higher among African American recruits with SCT compared to those without Hemoglobin S. 7 DoD's 1981 policy recommend screening to identify Hemoglobin S, confirmation of Positive screening tests with method able to quantify percentage of Hemoglobin S and define Hemoglobin phenotype, and lastly, consultation with medical personnel about implications of result. 5 in 1996, requirement for SCT screening was remove, when DoD instead adopted universal practices to prevent EHI. 6 Under circumstances similar to DoD, the NCAA mandates screening student athletes for SCT after EHI - related deaths. 8 in contrast to DoD policy, NCAA statement recommends the Sickle Solubility Test to screen for SCT without mention of confirmatory tests or post - Test education. 4 to examine tests used for Sickle Cell screening, we conducted PubMed and MeSH searches for terms Sickle Cell trait screening and Sickle Cell trait diagnosis. Keywords describing known testing methodologies were added to search terms. English language filter was applied to search. Search yielded 819 unique references, which were evaluated by title and keyword review for relevance. Following abstract review, commentaries, case reports, case series, and epidemiologic studies were eliminate. The remaining 55 articles determined to be relevant were reviewed for content. Additional articles were selected from commonly cited references therein. 21 references chosen for this review, including Table, were seminal articles about SCT and widely used tests to identify Hemoglobin S. We contacted the College of American Pathologists directly for current data on Solubility tests.

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Pathophysiology

Hemoglobin S arise AS result of point mutation in sixth codon of - globin gene on chromosome 11, which causes single amino acid substitution. Hemoglobin S is more positively charge than Hb and hence has different electrophoretic mobility. Deoxygenate Hemoglobin S polymerizes, leading to cellular alterations that distort red cell into rigid, sickled form. Vaso - occlusion with ischemia - reperfusion injury is central event, but underlying pathophysiology is complex, involving a number of factors including Hemolysis - associate reduction in Nitric Oxide bioavailability, chronic inflammation, oxidative stress, altered red Cell adhesive properties, activate White blood cells and platelets and increased viscosity. The following mechanisms are thought to be involve: Sickle cells are prematurely destroy, causing hemolytic anemia. Intravascular Hemolysis Reduces Nitric Oxide bioavailability by following mechanisms: release of arginase from red cells consumes plasma L - Arginine, substrate for NO production. Free plasma Hemoglobin reacts with NO, producing methemoglobin and nitrate, thereby depleting NO, increasing xanthine oxidase and NADPH oxidase activity in Sickle Cell disease, leading to production of Free oxygen radicals that consume NO. Figure 8 - 1. Intravascular Hemolysis Reduces Nitric Oxide Bioactivity. Nitric Oxide is produced by isoforms of Nitric Oxide synthase, using substrate L - Arginine. Intravascular Hemolysis simultaneously releases Hemoglobin, arginase and lactate dehydrogenase from red cells into blood plasma. Cell - Free plasma Hemoglobin stochiometrically inactivates NO, generating methemoglobin and inert nitrate. Plasma arginase consumes plasma L - Arginine to ornithine, depleting its availability for NO production. Ldh also released from red cell into the blood serum serves as AS surrogate marker for magnitude of hemoglobin and arginase release. No is also consumed by reactions with reactive oxygen species produced by high levels of xanthine oxidase activity and NADPH oxidase activity seen in Sickle Cell disease, producing oxygen radicals like peroxynitrite. Resulting decreased NO Bioactivity in Sickle Cell disease is associated with pulmonary hypertension, priapism, leg ulceration and possibly with nonhemorrhagic stroke. Similar pathobiology is seen in other chronic Intravascular hemolytic anemias. From: Kato GJ, Gladwin MT, Steinberg MH. Deconstructing Sickle Cell disease: Reappraisal of the role of Hemolysis in development of clinical subphenotypes. Blood Reviews. 2007; 21, with permission. No normally regulates vasodilation, causing increased blood flow and inhibits platelet aggregation. Thus, reduced NO bioavailability is thought to contribute to vaso - constriction and platelet activation. Adhesion molecules are overexpressed on Sickle reticulocytes and mature red cells. Increase red Cell Adhesion Reduces flow rate in microvasculature, trapping red cells contributing to vaso - occlusion. Sickle cells increase blood viscosity, which also contributes to vaso - occlusion. Sickle red cells may damage endothelium leading to production of inflammatory mediators. Ischemia - reperfusion also causes inflammation. White blood cell counts are often elevated in Sickle Cell disease and these white cells have increased adhesive properties. White blood cells adhere to endothelial cells and may further trap sickled red cells, contributing to stasis. Activated platelets may interact with abnormal red cells, causing aggregation and vaso - occlusion. Hemoglobin F affects HbS by decreasing polymer content in cells.


Introduction

Sickle cell disorder, also know as drepanocytosis, is a quadrumvirate of anemia and its sequelae, pain syndromes, organ damage including infection, and comorbid conditions. 1 - 6 It is a chronic blood disorder characterized by red blood cells that assume abnormal, rigid, sickle shape. Striking deformity of red blood cells leads to disorder being termed sickle cell anemia 7 and sickle cell disease, 8, names that reflect subsequent acceptance that erythrocyte distortion was central to development of its symptoms. In 1917, Emmel notes that the degree of erythrocyte deformation varies with time 9 and Hahn and Gillespie 7 demonstrate that this eponymous change was induced by deoxygenation. This disorder is usually present early in childhood and affects millions throughout the world. It occurs more commonly in people from parts of tropical and Sub - tropical regions where malaria is or was common. One - third of all aboriginal inhabitants of Sub - Saharan Africa, Spanish - speaking regions, Saudi Arabia, India, and Mediterranean countries such as Turkey, Greece, and Italy, carry gene. * This is because in areas where malaria is common, there is survival value in carrying only a single sickle - cell gene. Those with only one of two alleles of sickle cell disorder are more resistant to malaria, since infestation of malaria plasmodium is halt by sickling of cells which it infest. In the US, it affects around 72 000 people, most of whose ancestors come from Africa. 6 disorder occurs in about 1 in 500 African - American births and 1 in 1 000 - 1 400 Hispanic - American births. About 2 million Americans, or 1 in 12 African Americans, carry sickle cell trait. Scd is considered the most common monogenic disease in Brazil. As the generation of individuals with sickle cell disorders and thalassemia ages, new chronic complications of these hemoglobinopathies develop, several of which are potentially lethal and clinically multi - systemic with great variability of manifestations modulated by genetic and environmental factors. Early understanding of its pathological nature, sources, types, complications, pathophysiological basis, and clinical severity of symptoms among clinical psychologists, genetic counselors and psychotherapists, as well as general medical practitioners, could guide them in providing holistic care for dealing with and reducing pain among individuals living with SCD. However, there is little in literature concerning psychotherapeutic management of symptoms and crises of SCD. There are also limited numbers of trained clinical psychologists and genetic counselors to cater for psychotherapeutic needs of individuals living with disease. Even among those who have been train, only a few of them might have fully grasped the complexities of pathology of SCD. Hence, need for this paper.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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Structural Alterations in Hemoglobin

Sickle cell Hemoglobin is caused by a mutation that replaces glutamic acid at residue 6 in - Globin with valine. This amino acid substitution leads to the formation of linear polymers of deoxygenated HBS. Removal of O 2 from HBS in tissues exposes complementary sites that are also on the surface. Valine residue on the surface of HBS binds to a complementary site, linking two tetramers together. As more tetramers become link, linear polymers are formed that convert normally flexible RBCs into stiff, sickle - shaped cells. Inelastic, sickle - shaped cells plug capillary beds and precipitate sickling crisis. Note that the complementary site is not exposed to oxygenated blood, so sickling is initiated in peripheral tissues and joints. Hbs is the most common hemoglobin variant worldwide, since heterozygous form confers resistance to malaria. It occurs primarily in the black population of the United States, affecting 1 in 500 newborns. When mutation occurs on both chromosomes, it produces sickle cell disease; this has the most severe symptoms, since RBC has no source of normal - Globin. With mutation only on one chromosome, it produces sickle cell trait; production of nearly equal amounts of normal - Globin and S - Globin reduces the severity of symptoms by lowering the degree of sickling that occur. Hemoglobin C is caused by mutation at the same site as AS sickle cell Hemoglobin, except alteration is glutamate To lysine. Since lysine has little or no tendency to bind complementary site, no sicklings occur. Hb Boston is caused by tyrosine substitution close to heme iron; this stabilizes heme iron in oxidized form, preventing binding of O 2. Hb Boston is one of several hereditary methemoglobinemias that are characterized by cyanosis. Hb Chesapeake is caused by leucine substitution that weakens salt bridges, causing them to break more easily. The resulting increase in O 2 Affinity, resulting from decreased sensitivity to negative allosteric effectors, makes it more difficult for RBCs to unload O 2 in tissues, creating hypoxia. This signals an increase in RBC production and leads to polycythemia. Hb Koln is caused by methionine substitution that produces Unstable - Globin. Denaturation of hemoglobin eventually leads to RBC fragility and hemolytic anemia.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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