Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Neuronal ceroid lipofuscinosis wikipedia , lookup
Gene therapy wikipedia , lookup
Public health genomics wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Genetic code wikipedia , lookup
Cell-free fetal DNA wikipedia , lookup
Designer baby wikipedia , lookup
Expanded genetic code wikipedia , lookup
THALASSEMIAS AND HEMOGLOBINOPATHIES Modified from an original presentation by Raymond L. Olesinski ©2001 University of Kentucky Thalassemias and Hemoblobinopathies: Module Objectives At the end of this module you should be able to • Explain the pathophysiology that causes thalassemia and hemoglobinopathies. • Explain how thalassemias are categorized. Thalassemias and Hemoblobinopathies: Session Objectives • Correlate the results of laboratory testing with specific thalassemias and hemoglobinopathies. Thalassemias and Hemoblobinopathies: Session Objectives For the 1. Dithionite tube test 2. Hemoglobin electrophoresis 3. Alkali denaturation test for fetal hemoglobin • Discuss specifics of specimen collection, handling, storage, and preparation Thalassemias and Hemoblobinopathies: Session Objectives • • • • Explain the physiologic theory relevant to the test/procedure. Explain the principle of the test/procedure Identify the disease manifestation/clinical correlation. Differentiate or resolve technical, instrument, or physiologic causes of problems or unexpected test results. Characteristics: Thalassemia • • Hereditary disorders that can result in moderate to severe anemia Basic defect is reduced production of selected globin chains Demographics: Thalassemia • • Found most frequently in the Mediterranean, Africa, Western and Southeast Asia, India and Burma Distribution parallels that of Plasmodium falciparum Classification & Terminology Alpha Thalassemia • Terminology • • • • • Silent carrier Minima Minor Intermedia Major Symbolism Alpha Thalassemia • Greek letter used to designate globin chain: Symbolism Alpha Thalassemia / : Indicates division between genes inherited from both parents: / • Each chromosome 16 carries 2 genes. Therefore the total complement of genes in an individual is 4 Symbolism Alpha Thalassemia - : Indicates a gene deletion: -/ Classification & Terminology Alpha Thalassemia • Normal • Silent carrier • Minor • Hb H disease • Barts hydrops fetalis / - / -/- --/ --/- --/-- Symbolism Other Thalassemia • Greek letter used to designate globin chain: Symbolism Other Thalassemia +: Indicates diminished, but some production of globin chain by gene: + Symbolism Other Thalassemia 0 :Indicates no production of globin chain by gene: 0 Symbolism Other Thalassemia Superscript T denotes nonfunctioning gene: T Classification & Terminology Beta Thalassemia • Normal • Minor • Intermedia • Major / /0 /+ 0/+ 0/0 +/+ Special Cases Thalassemia • • Hb Lepore: fusion seen in some types of thalassemia Hb Constant Spring • chain with 31 additional amino acids • --/cs • Hereditary persistence of fetal hemoglobin (HPFH) Special Cases: Thalassemia • Hb H • 4 tetramer • Associated with --/- thalassemia Special Cases: Thalassemia • Hb Barts & hydrops fetalis • • • • Barts is a 4 tetramer Associated with --/-Lethal High concentrations are capable of sickling Primary Laboratory Investigation Thalassemia Variable hemogram results proportional to the severity of the thalassemia Primary Laboratory Investigation Thalassemia • Severe cases present with • • • • Microcytosis Hypochromia Poikilocytosis RBC counts higher than expected for the level of anemia Primary Laboratory Investigation Thalassemia • • • Findings in severe cases can mimic those seen in other microcytic/hypochromic anemias Results of the reticulocyte count are variable NRBCs may be present (contrast with iron deficiency anemia) Course and Treatment Thalassemia • Time of presentation • Related to degree of severity • Usually in first few years of life • Untreated severe thalassemia • • --/--: Prenatal or perinatal death --/- & --/cs: Normal life span with chronic hemolytic anemia Course and Treatment Thalassemia • Untreated thalassemia • • • Major: Death in first or second decade of life Intermedia: Usually normal life span Minor/Minima: Normal life span Characteristics: Hemoglobinopathies • • Hereditary disorders that can result in moderate to severe anemia Basic defect is production of an abnormal globin chain Demographics Hemoglobinopathies • The demographics of hemoglobinopathies are varied. Hemoglobinopathy Genetics • • Homozygous: Inheritance of two genes from each parent coding for the same type of abnormal hemoglobin, e.g., Hb SS Heterozygous: Inheritance of genes from each parent which code for a different type of abnormal hemoglobin each, e.g., Hb SC Terminology Hemoglobinopathy Abnormal hemoglobins discovered earlier have been given letter designations: Hb S Terminology Hemoglobinopathy More recently discovered hemoglobins have been named by the city or location of discovery: Hb C-Harlem Amino Acid Substitution Hemoglobinopathy Greek letter designates affected globin chain Amino Acid Substitution Hemoglobinopathy Superscript number designates affected amino acid(s), e.g., 6 Amino Acid Substitution Hemoglobinopathy Letters and numbers in parentheses designate the helical segment and amino acid sequence in that segment affected (sometimes omitted), e.g., 6(A3) Amino Acid Substitution Hemoglobinopathy Amino acid substitutions are denoted by the three letter abbreviation for the normally occurring amino acid followed by an arrow followed by the three letter abbreviation for the substituted amino acid: 6(A3)Glu Val Classification: Hemoglobinopathy • Functional Abnormality • Aggregation • • Polymerization Crystallization • Unstable hemoglobins • Methemoglobin • Oxygen affinity Primary Laboratory Investigation Hemoglobinopathy • Variety of hemogram findings depending on • Type • Severity • of the specific disorder Only sickle hemoglobinopathies and Hb C will be described here Primary Laboratory Investigation Heterozygous & Other Disorders • • • • AS S-Thal Other hemoglobinopathies, e.g., SC Hb C Morphologic Findings Hb SS vs. Hb SC vs. Hb CC = + Hb S Hb C Hb SC Morphologic Findings Hb SS vs. Hb SC vs. Hb CC = + Hb S Hb C + Hb SC = Where Do Sickle Cells Come From? Sheared in microcirculation Irreversible Sickle Cell Sickle Cells Secondary Laboratory Investigation • Hemoglobin electrophoresis • Major test for identifying thalassemia and hemoglobinopathy • Types • • Cellulose acetate: Alkaline pH Citrate agar: Acid ph Secondary Laboratory Investigation • Patterns of mobility (see handout) Secondary Laboratory Investigation Cellulose Acetate Hb Electrophoresis - A2/C Normal S F A+ Secondary Laboratory Investigation Cellulose Acetate Hb Electrophoresis - A2/C Normal Hb SS S F A+ Secondary Laboratory Investigation Cellulose Acetate Hb Electrophoresis - A2/C S Normal Hb SS Hb AS F A+ Secondary Laboratory Investigation Cellulose Acetate Hb Electrophoresis - A2/C Normal Hb SS Hb AS Hb SC S F A+ Secondary Laboratory Investigation Cellulose Acetate Hb Electrophoresis - A2/C Normal Hb SS Hb AS Hb SC Hb CC S F A+ Secondary Laboratory Investigation Cellulose Acetate Hb Electrophoresis - A2/C S Normal Hb SS Hb AS Hb SC Hb CC HB AD F A+ Secondary Laboratory Investigation • • • • Solubility testing-Dithionite tube test Alkali denaturation test for quantification of fetal hemoglobin Acid elution test for fetal hemoglobin distribution Unstable hemoglobin testing for Heinz bodies Alkali Denaturation for Hemoglobin F • • Recommended assay for hgb F in the range of 2-40% Principle • Other hemoglobins are more susceptible than hgb F to denaturation at alkaline pH • Denaturation stopped by addition of ammonium sulphate • Denatured hemoglobin precipitates Alkali Denaturation for Hemoglobin F • Remaining hemoglobin (F) can be measured spectrophotometrically • • Specimen: EDTA anticoagulated whole blood QC: Normal and elevated controls should be used with each batch of specimens Alkali Denaturation for Hemoglobin F Hgb F, % Diff. Between Duplicates, % <5 5-15 >15 0.5 1.0 2.0 Alkali Denaturation for Hemoglobin F • Sources of error • Too short or too long an incubation time • Filtrate turbidity • Outdated reagents • Incorrect reagent concentrations • Poor quality filter paper Acid Elution for Fetal Hemoglobin • • • Indication of distribution of fetal hemoglobin in a population of RBC Homogeneous distribution: hereditary persistence of fetal hemoglobin Heterogeneous distribution: thalassemia Course and Treatment Sickle Cell Disease • Sickle cell disease • Asymptomatic at birth • Symptoms appear as percentage of fetal hemoglobin decreases during first year of life • Untreated crises increase morbidity and early death Course and Treatment Sickle Cell Disease • Life span can be significantly increased with early and effective treatment • Studies of natural populations reveal that individuals with sickle cell disease are capable of normal life spans Course and Treatment In both thalassemia and hemoglobinopathy therapy is usually supportive rather than curative Course and Treatment • Blood transfusion is used to • Control severe anemia • Reduce the risk of complications of sickle hemoglobinopathies (cerebrovascular accident, hypersplenism, etc.) Course and Treatment • Chronic blood transfusion • Results in iron overload of major organs resulting in increased morbidity • Laboratory monitoring • Necessitates the use of chelating agents to remove excess iron Course and Treatment • Excess iron can cause the appearance of sideroblastic conditions • Transfusion interferes with the typical laboratory findings for the disorder Course and Treatment • Alternative treatment • Activation of fetal hemoglobin genes • Bone marrow transplantation WWW Sites of Interest Joint Center for Sickle Cell and Thalassemic Disorders: http://wwwrics.bwh.harvard.edu/sickle/ (Overview of sickle cell disease, thalassemia and iron kinetics) The Sickle Cell Information Center, Emory University: http://www.emory.edu:80/PEDS/SICKLE/ (Includes PowerPoint presentations on sickle cell disease)