Thalassemias1 HEMOGLOBIN A α β β α Fetal Hemoglobin (2 alpha, 2 gamma) Hemoglobin A2 (2 alpha, 2 delta) Small amounts in body Disorders of Haemoglobin 1. Thalassemia 2. Haemoglobinopathies What is Thalassaemia ? Thalassaemia is a group of inherited disorders of hemoglobin synthesis characterized by a reduced or absent one or more of the globin chains of adult hemoglobin . Genetic autosomal recessive blood disease. The name is derived from the Greek words Thalasso = Sea" and "Hemia = Blood" in reference to anemia of the sea. Thalassemia ► Mediterranean Anemia’- 1st published in 1925 ► May be either homozygous defect or heterozygous defect. 5 Thalassemia ► Results in overall decrease in amount of hemoglobin produced and may induce hemolysis. ► May contribute protection against malaria. 6 Demographics: Thalassemia • Found most frequently in the Mediterranean, Africa, Western and Southeast Asia, India and Burma GeneticTypes of Thalassaemia : There are two basic groups of thalassaemia. Alpha ( )Thalassaemia Beta ( )Thalassaemia Clinical Types of Beta Thalassaemia : There are 3 types of Beta thalassaemia : 1. Thalassaemia Minor 2. Thalassaemia Intermediate 3. Thalassaemia Major Genetics of Thalassemia ► Adult hemoglobin composed two alpha and two beta chains. ► Alpha thalassemia usually caused by gene deletion; Beta thalassemia usually caused by mutation. ► Results in microcytic, hypochromic anemias of varying severity. 10 Normal Human Haemoglobins Haemoglobin Structural formula Adult Hb-A Hb-A2 2 2 97% 2 2 1.5-3.2% Fetal Embryonic Hb-F Hb-Gower 1 Hb-Gower 2 Hb-Portland 2 2 2 2 2 2 2 2 0.5-1% Chromosomes Gene Structure ( Alpha 1 and Alpha 2 produce identical chains) ALPHA THALASSEMIA Alpha Thalassemia: deficient/absent alpha subunits Excess beta subunits Excess gamma subunits newborns Tetramers formed: Hemoglobin H adults Hemoglobin Bart’s newborns β/γ β/γ Five types: Silent Carrier Trait (Minor) Hemoglobin H Disease Major (Hemoglobin Bart’s) Hemoglobin Constant Spring β/γ β/γ GENETIC BASIS OF ALPHA THALASSEMIA Encoding genes on chromosome 16 (short arm) Each cell has 4 copies of the alpha globin gene Each gene responsible for ¼ production of alpha globin 4 possible mutation states: Loss of ONE gene silent carrier Loss of TWO genes thalassemia minor (trait) Loss of THREE genes Hemoglobin H Accumulation of beta chains Association of beta chains in groups of 4 Hemoglobin H Loss of FOUR genes Hemoglobin Barts NO alpha chains produced ∴ only gamma chains present Association of 4 gamma chains Hemoglobin Barts Classification & Terminology Alpha Thalassemia • Normal • Silent carrier • Minor • Hb H disease • Barts hydrops fetalis / - / -/- --/ --/- --/-- CLINICAL OUTCOMES OF ALPHA THALASSEMIA Silent carriers • asymptomatic • “normal” Alpha Thalassemia minor (trait) • no anemia • microcytosis -unusually small red blood cells due to fewer Hb in RBC • “normal” Alpha Thalassemia intermedia (“Hemoglobin H”) • microcytosis & hemolysis (breakdown of RBC) - results in severe anemia • bone deformities • splenomegaly (enlargement of spleen) • “severe and life threatening” CLINICAL OUTCOMES OF ALPHA THALASSEMIA Alpha Thalassemia major Hb Bart’s • fatal hydrops fetalis - fluid build-up in fetal compartments, leads to death • • occurs in utero BETA THALASSEMIA Beta Thalassemia: deficient/absent beta subunits Commonly found in Mediterranean, Middle East, Asia, and Africa Three types: Minor Intermedia Major (Cooley anemia) May be asymptomatic at birth as HbF functions GENETIC BASIS OF BETA THALASSEMIA Encoding genes on chromosome 11 (short arm) Each cell contains 2 copies of beta globin gene beta globin protein level = alpha globin protein level Suppression of gene more likely than deletion 2 mutations: beta-+-thal / beta-0-thal “Loss” of ONE gene thalassemia minor (trait) “Loss” of BOTH gene complex picture 2 beta-+-thal thalassemia intermedia / thalassemia major 2 beta-0-thal thalassemia major beta-+-thal / beta-0-thal thalassemia major Excess of alpha globin chains Classification & Terminology Beta Thalassemia • Normal • Minor • Intermedia • Major / /0 /+ 0/+ +/+ 0/0 +/+ 0/+ CLINICAL OUTCOMES OF BETA THALASSEMIA Beta Thalassemia minor (trait) • • • Beta Thalassemia intermedia • asymptomatic microcytosis minor anemia symptoms similar to Cooley Anemia but less severe Beta Thalassemia major (Cooley Anemia) • • • • • • • most severe form moderate to severe anemia intramedullary hemolysis (RBC die before full development) peripheral hemolysis & splenomegaly skeletal abnormalities (overcompensation by bone marrow) increased risk of thromboses pulmonary hypertension & congestive heart failure Thalassemia major Thalassemia minor Pathophysiology Disturbance of ratio between Alpha & non alpha globin chain synthesis then absent or decrease production of one or more globin chains Formation of abnormal Hb structures Ineffective erythropoiesis Excessive RBCs Destruction Iron Overload Extra-medullary hematopoiesis Signs & Symptoms Thalassaemia Minor : Usually no signs or symptoms except for a mild anemia. Thalassaemia Major : 1. Paleness, Jaundice or yellow coloured skin. 2. Growth retardation. 3. Bony abnormalities specially of the facial bones. 4. Enlarged spleen and liver. Laboratory Diagnosis of Thalassemia 36 Laboratory Diagnosis Thalassemia minor: Haemoglobin : Haemoglobin level is usually normal or mildly reduced. Peripheral blood film : Hypochromia and Microcytosis (similar to Iron Deficiency Anemia). MCV< 75 fl, RDW < 14%. Reticulocyte Count increases Decrease Osmotic Fragility Haemoglobin electrophoresis HPLC (High Performance liquid chromatography) Haemoglobin electrophoresis A F S C Other Special Procedures ► Globin Chain Testing - determines ratio of globin chains being produced. ► DNA Analysis - Determine specific defect at molecular DNA level. 41 Course and treatment of thalassaemia Untreated thalassemia Major : Death in first or second decade of life Intermedia: variable life span Minor/Minima: Normal life span TREATMENTS FOR ALPHA THALASSEMIA Silent Carrier – no treatment required Trait (Minor) – no treatment required Hemoglobin H Disease – Folate avoid iron supplements Major (Hemoglobin Bart’s) –RBC transfusion while still in womb, else fetus is stillborn or dies shortly TREATMENT FOR BETA THALASSEMIA Trait – no treatment required Intermedia Major (Cooley anemia) Regular folate supplementation RBC transfusion (Splenectomy may decrease need for transfusions) to maintain [Hgb] ~9-10g/dL Blood transfusions iron accumulation iron overload Iron chelators (diferroxamin)