Lecture 3 - Hemoglobinopathies

Hemoglobinopathies DR: Ghada A Abdel-Aleem Professor of medical biochemistry & molecular biology 1 Types of HB 3 Hb-A Molecule. Hb-A is the major adult hemoglobin. 4 5 Hemogl...

Hemoglobinopathies DR: Ghada A Abdel-Aleem Professor of medical biochemistry & molecular biology 1 Types of HB 3 Hb-A Molecule. Hb-A is the major adult hemoglobin. 4 5 Hemoglobinopathies ?  What are they? Disorders where the production of normal adult hemoglobin in partly or completely suppressed or replaced by a variant hemoglobin. 6  Hemoglobinopathies  Catagories Inherited abnormality of the structure of one or more of the globin chains Inherited abnormality related to the rate of synthesis of one or more of the globin chains Failure of the normal switch from fetal hgb (HbF) to adult hgb (HbA) 7  Qualitative: Hemoglobins differ in sequence of amino acids composing globin chain Disorders called hemoglobinopathies  Quantitative: Characterized by decreased production of hemoglobin resulting from decreased synthesis of one particular globin chain Called thalassemia 8  Qualitative abnormalities in globin structure, usually involving beta-chain.  Heme portion is normal  Arise from single amino acid substitution or deletion Rarely see multiple substitutions.  May or may not cause abnormal laboratory test results. 9 Sickle Cell Anemia & Sickle Cell Trait 10  Introduction to Sickle Cell Anemia  Most common hemoglobinopathy  Autosomal recessive  Hemoglobin A and Hemoglobin S produced.  AS is sickle cell trait.  SS is sickle cell disease.  Patient is homozygous for HbS (SS).  Results in very severe anemia. 11 Frequency  African Americans Sickle cell disease occurs in 0.3-1.35% Sickle cell trait occurs in 8-10%  Is worldwide disorder 12 How and Why Cells Sickle?  Hb S forms from a point mutation for the sixth amino acid in the Beta chain.  Valine substituted for glutamic acid.  One benefit for AS persons is increased resistance to malaria 13 14 Sickle Cell Anemia – blood film Sickle Cells Erythroblasts Howell-Jolly Body 15  Pathophysiology of Sickle Cell Anemia  SS cells may look normal when fully oxygenated; Sickling occurs when O2 decreased.  Other causes of sickling include decrease in pH, High altitude, Increased pCO2, Increased concentration of 2,3 BPG and dehydration of patient.  Cells become rigid, impeding blood flow to tissues. Tissue death, organ infarction, and pain result.  Sickling is reversible up to a point.  Have both extravascular hemolysis and intravascular hemolysis. 16 17 18 Deoxygenated Hb A deoxygenated Hb S Oxygenated Hb S NO present present Sticky patch present present masked complement 19 Clinical Findings of Sickle Cell Anemia  Clinical signs appear at 6 months of age  Have all physical symptoms of anemia  Growth and sexual maturation slower  Crisis – very painful. Anything that deoxygenates blood acts as trigger (exercise, illness and airplane flights). Sickle cells get stuck in capillaries.  Strokes 20  Sickle Cell Anemia: Clinical features  Organs Affected: Liver: Enlarges, malfunctions, jaundice, hyperbilirubinemia Heart: Cardiomegaly, iron deposits Spleen: Enlarges leading to infarction and fibrosis Eventually shrivels and becomes nonfunctional Skin: Develop ulcers, jaundice Kidney: Hematuria and eventual failure Lungs: Infarction Brain: Strokes Blood: Hemolytic anemia 21  Special Hematology Tests in Sickle Cell Anemia  Electrophoresis on cellulose acetate Hb S present @ 85-100%  Osmotic Fragility – Decreased 22  Chemistry Tests in Sickle Cell Anemia HemoBilirubin (Before entering lever)  Bilirubin – increased  Haptoglobin decreased 23  Sickle Cell Anemia: Treatment  Prevention of infection  Reduce organ damage Hydroxyurea (it is believed to induce production of Hgb F). Using chemotherapeutic agents. Avoidance of situations that could cause a crisis.  Minimize pain Blood transfusion  Median age at death Male: 42 Female: 48 24  Sickle Cell Trait  Heterozygous AS with more HbA than HbS, so condition is compensated for  Patient often has normal life span  Usually asymptomatic with occasional episodes of hematuria Sickling can occur with drastic reduction of oxygen tension such as severe respiratory infection, air travel in unpressurized aircraft, anesthesia or congestive heart failure Exercise that causes a buildup of lactic acid can cause sickling due to lowered pH 25 Laboratory Features: Sickle Cell Trait  Normal CBC – Few target cells or sickle cells may be present.  Electrophoresis – Both A and S present. 26  1 - What is the most common hemoglobin variant found in people of African descent with sickle cell trait? A) Hemoglobin A2 B) Hemoglobin S C) Hemoglobin C D) Hemoglobin F 2- What is the significance of finding both Hemoglobin A and Hemoglobin S in a patient’s electrophoresis pattern? A) The patient has sickle cell disease B) The patient has sickle cell trait C) The patient has beta-thalassemia D) The patient has hemoglobin C disease 27  HbC (glu lys)  Rare patients homozygous for HbC have a relatively mild, chronic hemolytic anemia with no infarctive crises  when both are present, HbSC causing a sickling disorder resembling homozygous HbS disease but less frequent and less sever. 28 Met Hbemia (Hb M) 29  Classical drug causes of methemoglobinemia various antibiotics (trimethoprim, sulfonamides, dapsone),  Localaanesthetics (especially articaine, benzocaine, prilocaine, and lidocaine), and aniline dyes, , chlorates, bromates, and nitrites. Nitrates are suspected to cause methemoglobinemia.  Nitrates used in agricultural fertilizers may leak into the ground and may contaminate well water. The current EPA standard of 10 ppm nitrate-nitrogen for drinking water is specifically set to protect infants. Benzocaine applied to the gums or throat (as commonly used in baby teething gels, or sore throat lozenges) can cause methemoglobinemia. 30 Item HbA HbM Iron Fe+2 Fe+3 5th coordination Histidine Tyrosine 6th coordination Oxygen Water 32  THALASSEMIAS  The thalassemias are the result of abnormalities in hemoglobin synthesis and affect both clusters.  Deficiencies in β-globin synthesis result in the β- thalassemia and deficiencies in α-globin synthesis result in the 33  β-Thalassemias  A large number of mutations have been identified leading to decreased or absent production of β-globin chains resulting in the β-thalassemias. (Point mutations)  Alpha chains production is normal  But cannot form stable tetramers  And precipitate and prematurely cells die without forming RBCs. 35  If both the beta globin genes are defective then it is called Thalassemia major.  Thalassemia major patients require frequent blood transfusions for survival.  Thalassemia minor patients are heterozygous for β-thalassemia. Afflicted individuals harbor one normal β-globin gene and one that harbors a mutation leading to production of reduced β-globin. 36 Clinical and Hematological Findings  At birth most thalassemia major infants are asymptomatic. However, because fetal hemoglobin (HbF) production declines following birth symptoms of severe anemia will begin to present.  If left untreated these children will show a marked retardation in growth rate. As a consequence of the anemia the bone marrow dramatically increases its effort at blood production. 37  The cortex of the bone becomes thinned leading to pathologic fracturing and distortion of the bones in the face and skull.  Progressive hepatosplenomegaly is a constant clinical finding as the liver and spleen act as additional sites of blood production. 38  The hepatosplenomegaly leads to leukopenia (decreased white blood cell count) and thrombocytopenia (low platelet count).  Recurrent infections are a frequent complication in thalassemia major and are the leading cause of morbidity and mortality in this disease. 39 Frequent blood transfusions are required to maintain a hemoglobin level of 9 to 11g/dl. In the long term these transfusions lead to the accumulation of iron in the organs, particularly the heart, liver and pancreas. Organ failure ensues with death in the teens to early twenties. Iron chelation therapies appear to improve the outlook for β-thalassemia major patients but this requires continuous infusion of the chelating agent. 40 41 42  α-Thalassemias  With the α-thalassemias the level of α-globin production can range from none to very nearly normal levels. (Deletional mutations)  This is due in part to the fact that there are 2 identical α-globin genes on chromosome 16. Thus, the α-thalassemias involve inactivation of 1 to all 4 α-globin genes. 43  If 3 of the 4 α-globin genes are functional, individuals are completely asymptomatic. This situation is identified as the "silent carrier" state.  If 2 of the 4 genes are inactivated individuals are designated as "α- thalassemia trait" 44  The clinical situation becomes more severe if only 1 of the 4 α-globin genes is functional.  Because of the dramatic reduction in α- globin chain production in this latter situation, a high level of β4tetramer is present. Clinically this is referred to as hemoglobin H disease (HbH). 45  The most severe situation results when no α-globin chains are made.This leads to prenatal lethality or early neonatal death.  The predominant fetal hemoglobin in afflicted individuals is a tetramer of γ- chains and is referred to as hemoglobin Bart's.. 46  This hemoglobin has essentially no oxygen carrying capacity resulting in oxygen starvation in the fetal tissues.  Heart failure results as the heart tries to pump the unoxygenated blood to oxygen starved tissues leading to marked edema. This latter situation is called hydrops fetalis. 47 1- Which of the following is the cause of α- thalassemia? a. Deletion of alpha gene b. Deletion of beta gene c. Excess of alpha gene d. Single amino acid substitution in alpha chain 2-In hydrops fetalis with Hb Bart’s how many of the 4 α globin loci are deleted; 1 2 3 4 48 1- In which condition would you expect to see a high proportion of Hemoglobin F in an adult patient’s hemoglobin electrophoresis results? A) Beta-thalassemia major B) Sickle cell trait C) Iron deficiency anemia D) Hemoglobin C trait 2- A newborn's hemoglobin electrophoresis shows high levels of Hemoglobin F What is the most likely interpretation? A) The child has sickle cell disease B) This is a normal finding C) The child has thalassemia major D) The child has hemoglobin C disease 49  Learning Resources  Lecture notes  Lippincott’s Illustrated Reviews: Biochemistry 50