HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESPart 1

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESHemolytic anemias are a heterogenous group of normochromic, normocytic anemias (except for the thalassemias) in which the RBC survival time is decreased.The premature destruction may result from intrinsic abnormalities of the RBCs or abnormalities extrinsic to the RBC.Reticulocytosis is a constant feature.

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESRemember that the life span of the RBC can decrease to about 18 days before increased erythropoiesis in the bone marrow is unable to compensate. Hemoglobinopathies are a type of intracorpuscular defect leading to the production of an abnormal hemoglobin or to an aberration of hemoglobin synthesisAbnormal hemoglobinsMost are clinically insignificant with no physiologic consequence

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESMost abnormalities occur in the beta chain with abnormalities in this chain more likely to cause disease because we have only two genes that encode the beta chains, but we have four genes that encode the alpha chains.Most variants arise from the substitution of a single amino acid in the globin chain.

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESChanges may also arise from multiple substitutions, insertions or deletions, frame shift mutations, cross-overs, and fusions of subunits.If an individual is homozygous for a structural gene in the beta chain, the individual is said to have the disease or anemiaIf the individual is heterozygous, they are said to have the trait, and 50% or less of the hemoglobin will be abnormal.The % of abnormal hemoglobin is usually less than 50% because the chain will preferentially bind with the normal chains.

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESSickle cell diseaseHemoglobin S position 6 on the chain has a valine (nonpolar) substituted for the normal glutamic acid (polar)Carriers of the gene in Africa may be as high as 20-40% because when parasitized by Plasmodium (causes malaria), cells containing hgbS will sickle quickly, either killing the parasite or causing RBCs to be sequestered in the spleen and destroyed. Therefore, having the gene provides a certain protection against malaria.It is usually only in the homozygous state that the disease is so devastating8-10 % of African Americans are carriers in the U.S., with .3-1.3 % being homozygous

HEMOGLOBIN S

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESPathophysiology of the diseaseWhen oxygenated, Hgb S is solubleWhen oxygen tension decreases, hgb S in the deoxyhemoglobin state polymerizes into insoluble aggregates leading to sickled cellsThis leads to increased blood viscosity which leads to decreased circulation and increased exposure to low oxygen. This, in turn, leads to more sicklingThe small microvasculature may become clogged with the rigid sickle cells leading to hypoxia and infarction of organs and a sickle cell crisis.

SICKLE CELLS

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESUpon reoxygenation, the RBC may return to its original shapeHowever, repeated sickling damages the permeability of the RBC membrane leading to premature death of the cellIn addition, after repeated sickling events, the cells become irreversibly sickled and are removed by the spleenEarly in childhood, the spleen loses its function due to splenic atrophy and necrosis from repeated ischemic (blood supply decreased due to blockage of the small vasculature) crises. Thus, these young patients are more prone to infections, especially from encapsulated microorganisms. The liver and bone marrow then take over destruction of abnormal cells.

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESHgb S has a decreased affinity for oxygen, leading to a shift to the right in the oxygen dissociation curve. This, however, creates more deoxyhemoglobin, and hence, more sicklingClinical findingsThe disease is diagnosed early at about 6 months of age when hemoglobin F is replaced with hgb S rather than hgb A.Homozygous individuals frequently do not live beyond middle age (improved healthcare has increased the life expectancy of these individuals)Chronic hemolytic anemia due to extravascular hemolysis.RBC survival may decrease to 14 daysIncreased bilirubin turnover leads to gallstones

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESCompensation mechanisms lead to cardiac hypertrophy and enlargement and eventual failureThe hyperplastic bone marrow leads to thinning of the bonesHematologic complications that may occur are called crises. Three types of crisis may occurAplastic usually associated with infection and results in temporary marrow aplasia due to overworkHemolytic crisis sudden acute anemia in young children this may be due to splenic poolingVaso-occlusive or painful plugs of rigid sickle cells in the capillaries cause tissue damage and necrosis and lead to organ dysfunction. This is the hallmark of sickle cell disease.

VASO-OCCLUSIVE CRISIS

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESLab findingsNormochromic, normocytic anemia10-20% reticulocytes6-10 g/dl hgbDuring crisis marked anisoctyosis and poikilocytosis with target cells, fragmented cells, nucleated RBCs, and sickle cellsBasophilic stippling, Howell Jolly bodies and siderocytes due to splenic hypofunctionBone marrow normoblastic hyperplasiaDiagnosis by a peripheral smear, hgb electrophoresis, solubility tests, sodium metabisulfite will cause the cells to sickle by deoxygenating the blood (seen under the microscope)

SICKLE CELL DISEASE

HEMOGLOBIN ELECTROPHORESIS

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESTherapyNo known effective long term therapyDrug companies are working on drugs to inhibit hgb S polymerizationBone marrow transplantGene therapySickle cell trait heterozygous for hgb SUsually the patient has no problems because >50% of their hemoglobin is hgb AThere may be occasional problems upon exposure to severe hypoxiaDiagnosis is by hgb electrophoresis or sodium metabisulfite treatment

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESHemoglobin C diseaseLysine is substituted for glutamic acid at position 6 on the chain.Hgb C has decreased solubility and in the deoxyhemoglobin state, the RBCs form intracellular crystals leading to a rigid RBC with a decreased survival time (33-35 days).The disease is usually asymptomatic although patients may have joint or abdominal pain.This disease is common in Africa.

HEMOGLOBIN C

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESLab findingsSlight reticulocytosisHgb C crystalsTarget cellsRBCs may look foldedMicrospherocytes Fragmented cellsDiagnosis by hgb electrophoresis

HEMOGLOBIN C DISEASE

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESHgb C trait is symptomlessS/C diseaseBoth chains are abnormalTherefore, hgb A is absent and the disease is almost as severe as in hgb S diseaseClinical symptoms are similar to those of mild sickle cell anemiaThe patient may develop a vaso-occlusive crisisDifferential diagnosis of S/C from hgb S disease may be made on the finding of prominent splenomegaly in S/C disease. Why is this not seen in hgb S disease?

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESLab findingsNormochromic, normocytic mild to moderate anemiaMany target cells, folded cells, cells with hgb C crystals, and occasional sickle cellsSlight to marked anisocytosis and poikilocytosisDiagnosis using hgb electrophoresis

S/C DISEASE

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESHgb D disease and traitA glutamine replaces glutamic acid at position 121 on the chainBoth homozygous and heterozygous states are asymptomaticWhen combined with S to form D/S, D potentiates the polymerization of deoxyhemoglobin leading to sickling and mild anemia.Hgb E disease and trait

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESA glutamic acid replaces lysine at position 26 on the chain leading to a slightly unstable hemoglobin with oxidant stress.Hgb E has a decreased affinity for oxygen leading to a shift to the right in the oxygen dissociation curveThis is found mainly in individuals from the OrientHomozygous individuals have a mild microcytic anemia with decreased RBC survival, target cells and increased osmotic fragilityHeterozygous individuals are symptomlessUnstable hemoglobin disordersContain amino acid changes in internal portions of he hgb chains leading to decreased stabilityThey are characterized by precipitation of the abnormal hgb as Heinz bodies which leads to increased cell rigidity, membrane damage, and RBC hemolysis.

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESThese hgb disorders are known collectively as congenital Heinz body hemolytic anemiasThey are only found in the heterozygous state since the homozygous state is incompatible with lifeHemoglobin variants with altered oxygen affinity

HEMOLYTIC ANEMIAS THE HEMOGLOBINOPATHIESAmino acid substitutions in the globin chains close to the heme pocket may affect the ability of the hemoglobin to carry oxygenThis also occurs with substitutions near the 2, 3 DPG binding siteDecreased hgb affinity for oxygen leads to the shift to the right in the oxygen dissociation curveIncreased oxygen affinity leads to a shift to the left in the oxygen dissociation curve and to polycythemiaHgb M variantsAre characterized by permanent methemoglobin formation because iron is stabilized in the Fe +3 state

HEMOGLOBINS WITH ALTERED AFFINITY FOR OXYGEN