George R. Honig Junius G. Adams III Human Hemoglobin Genetics Springer-Verlag Wien New York
George R. Honig, M.D., Ph.D. Professor and Head Department of Pediatrics, College of Medicine University of Illinois Chicago, Illinois, U. S. A. Junius G. Adams III, Ph.D. Chief, Hemoglobin Research Laboratory, VA Medical Center, and Associate Professor, Department of Medicine University of Mississippi School of Medicine Jackson, Mississippi, U. S. A. This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. 1986 by Springer-Vedag/Wien Softcover reprint of the hardcover 1 st edition 1986 With 123 Figures (1 in color) Library of Congress Cataloging-in-Publication Data. Honig, George R., 1936-. Human hemoglobin genetics. I. Hemoglobinopathy - Genetic aspects. 2. Hemoglobin. 3. Human genetics. I. Adams, Junius G., 1943-. II. Title. [DNLM: I. Hemoglobinopathies - familial & genetic. 2. Hemoglobins - genetics. WH 190 H773h] RC641.7.H35H66. 1986. 616.1.'51. 85-14704 ISBN-13: 978-3-7091-8800-2 DOl: 10.1007/978-3-7091-8798-2 e-isbn-13: 978-3-7091-8798-2
To Paul Heller, M.D., our teacher, colleague and friend
Preface The discovery in the late 1940's that sickle cell anemia is a "molecular disease" of hemoglobin was the crucial advance that gave birth to the scientific discipline of human molecular genetics. In subsequent years, with the continued expansion of knowledge about the biology and genetics of the hemoglobins, and particularly as a result of the characterization of the very large numbers of globin gene mutations, the human hemoglobin system has remained as the premier model of gene expression at the molecular level in man. With the recent explosion of new information about the genetic properties of the hemoglobins, it appears inevitable that this gene system will continue to occupy a unique position in human molecular genetics for many years in the future. Hemoglobin genetics has also recently come of age as a diagnostic and clinical discipline. The heightening of public awareness in recent years about sickle cell disease, thalassemia, and other inherited disorders has brought increasing demands for carrier detection services as well as for genetic counseling and education. The more recent development of practical and reliable methods for the antenatal diagnosis of hemoglobin disorders has further increased the scope of clinical hemoglobin genetics, and it can be anticipated that these potent diagnostic techniques will have increasing application in the years ahead. Other recent advances, which have made possible the development of effective forms of treatment for patients with hemoglobin-related disorders, hold promise for what may well be the most significant applications of human hemoglobin genetics. Chemotherapy and bone marrow transplantation have already been shown to be capable of producing dramatically beneficial effects in these patients, and generally applicable forms of treatment now seem likely to become a reality within the foreseeable future. In a recent editorial Benz (1982), commenting on the rapidity with which molecular genetics is achieving clinical relevance, concluded that "The era when the physician will require a working knowledge of this discipline and an ability to apply its power is no longer approaching; it is here." In preparing this monograph we have endeavored to develop a concise but relatively detailed account of the current state of understanding of the human hemoglobin system and the genetic and biological factors that
VIII Preface govern its expression. Its content is directed toward the medical geneticist, the genetic counselor, and the health educator as well as physicians, nurses, and others in the health professions who seek an introduction to this area of human genetics. We hope that this book will also meet the needs of students and others who require a more extensive account of human hemoglobin genetics than will be found in standard genetics texts. We are indebted to numerous friends and colleagues for helpful discussions and contributions of data, and for providing many of the illustrations. The manuscript was patiently typed and organized by Fran Flaminio and Sandy Alvord. Chicago, Ill., and Jackson, Miss., November, 1985 George R. Honig Junius G. Adams III
Contents 1. Introduction 1 A. The Hemoglobins in Human Biology and Genetics - An Overview 1 B. Historical Foundations of Human Hemoglobin Genetics 4 1. Early Genetic Studies of Sickle Cell Anemia and Thalassemia 5 2. Abnormal Hemoglobins as Molecular Diseases 7 3. The Genetic Basis of the Thalassemias 12 4. Discoveries of Additional Globin Genes and Linkage Relationships 13 5. Methodological Advances in Hemoglobin Research 15 2. The Human Hemoglobins 19 A. Hemoglobin Structure and Function 19 1. The Structure of the Hemoglobin Molecule and Its Subunits 19 2. Hemoglobin Function and Its Control 26 B. The Normal Human Hemoglobins and Their Globin Subunits 29 1. The Globin Polypeptide Chains 29 2. The Normal Human Hemoglobins 33 3. The Hemoglobins in Gestation and Development 35 3. The Human Globin Genes 37 A. DNA Structure and Function 37 B. Recent Methodologic Advances in the Study of Genes and Their Structure 40 C. Globin Gene Localization and Organization 48 1. The Chromosomal Location of the Globin Genes 48 2. The Linear Arrangement of the Globin Genes in the Chromosomes 50 a) The ~-Gene Cluster 50 b) The a-gene Cluster 53
x Contents D. The Structure of the Globin Genes 53 1. Globin Gene Organization: Coding and Intervening Sequences 53 2. Flanking Regions of the Globin Genes and Their Role in Gene Transcription 58 3. The DNA Sequences of the Globin Genes 59 a) The a-gene Family 59 b) The ~-Gene Family 62 E. The Evolution of the Globin Genes 66 4. Hemoglobin Synthesis and Globin Gene Expression 73 A. Hemoglobin Synthesis and Its Regulation 73 1. Transcription of the Globin Genes 74 a) The Composition and Structure of Nuclear Chromatin 74 b) Properties of Transcriptionally Active Chromatin 75 c) Chromosomal Proteins and Gene Transcription 77 d) Regulation of Gene Transcription 78 e) Synthesis of the Primary Gene Transcript 79 f) Processing of the mrna Precursor 79 i) The Splicing Reaction 80 ii) The 5'-terminal Cap 82 iii) Polyadenylation of the mrna Precursor 84 g) Structure and Properties of the Human Globin mrna's 84 2. Globin Translation and Its Regulation 86 a) Translation Initiation 89 b) Polypeptide Chain Elongation and Termination 90 c) Heme Synthesis and Its Regulation 91 d) Regulation of Globin Chain Translation and the Role of Heme 93 e) Coordination of the Synthesis of the a- and non-a Globin Chains 95 B. Regulation of the Expression of the Normal Globin Genes 97 1. The a-globin Gene Group 97 2. Expression of the ~- and a-globin Genes 99 3. Gene Switching and Its Regulation 102 a) Globin Gene Switching in Embryonic and Fetal Development 102 b) y-globin Gene Expression in the Older Child and Adult 108 c) Elevated Levels of Hb F in Post-Infancy Development 110 d) Genetic Factors in Hb F Expression 112
Contents XI 5. The Globin Gene Mutations - A. Mechanisms and Classification 115 A. Mechanisms of Globin Gene Mutation 116 1. Single Base Changes ("Point Mutations") 116 2. Genetic Recombination 117 3. Nucleotide Deletions and Insertions 121 B. Classification of the Globin Gene Mutations 124 1. Mutations Associated with Globin Structural Abnormalities 124 a) Single Point Mutations which Produce Amino Acid Substitutions 124 b) Double Point Mutations 128 c) Point Mutations Causing Premature Translation Termination 130 d) Point Mutations Producing Extended Globin Chains 131 e) Deletion and Insertion Mutants 132 f) Frame Shift Mutants 133 g) Fusion-Gene Mutants 134 h) Complex Globin Gene Mutations 141 2. The Thalassemia Mutations 142 a) Gene-Deletion Thalassemia Mutations 143 i) a-globin Gene Deletions 143 ii) a-globin Gene Deletions in Association with a Chain Structural Mutants 145 iii) Deletions Involving the ~-Globin Gene Complex 146 b) The "Non-Deletion" Thalassemia Mutations 149 i) Mutations Affecting Globin Gene Transcription 150 ii) Base Substitution Involving the Translation Initiation Codon 151 iii) Mutations Producing Premature Termination Co dons 151 iv) Splice Junction Mutations 154 v) Mutations Producing Abnormal Splicing Sites 155 vi) Polyadenylation/Transcription-Termination Signal Mutations 157 3. Hereditary Persistence of Fetal Hemoglobin (HPFH) Mutations 158 4. Globin Gene Somatic Mutations 160
XII Contents 6. The Globin Gene Mutations - B. Their Phenotypes and Clinical Expression 163 A. Sickle Cell Disease 163 1. Pathogenesis 163 2. Hematological and Clinical Features 168 3. The Sickle Cell Disease Syndromes 169 4. Heterozygous Hb S (Sickle Cell Trait) 172 5. Hb F and Sickle Hemoglobin Expression 173 6. Other Genetic Abnormalities that Affect the Expression of Sickle Cell Disease 174 B. Intracellular Hemoglobin Crystallization: Hb C 175 C. Erythrocytosis: Abnormal Hemoglobins with Increased Oxygen Affinity 175 D. Congenital Cyanosis 181 1. Abnormal Hemoglobins with Low Oxygen Affinity 181 2. The Hb M Variants 182 E. Hemolytic Anemia ("Congenital Heinz-Body Anemia"): The Unstable Hemoglobins 186 F. The Thalassemias 191 1. Pathogenesis 191 2. The Phenotypes of the Thalassemia Syndromes 193 a) The a-thalassemia Syndromes 193 b) Structural Hemoglobin Variants with a-thalassemia-like Expression 199 c) The ~ Thalassemia Syndromes 201 d) Structural Hemoglobin Variants that are Expressed as ~ Thalassemia 204 e) a Thalassemia/~ Thalassemia Syndromes 205 f) The 0 Thalassemias 206 g) Thalassemia/Abnormal Hemoglobin Syndromes 206 G. The Syndromes of Hereditary Persistence of Fetal Hemoglobin 209 1. The Phenotypes of the HPFH Syndromes 209 2. Hereditary Persistence of Fetal Hemoglobin in Combination with Thalassemia or Structural Hemoglobin Variants 212 3. Chromosomal Abnormalities Associated with a Prolongation or Delay of Hemoglobin Switching 213 H. Precocious Synthesis of Adult Hemoglobin 213
Contents XIII 7. The Genetics of the Human Globin Gene Loci: Formal Genetics and Gene Linkage 215 A. The Formal Genetics of the Human Hemoglobin System 215 1. The ~-Globin Locus 216 2. The o-globin Locus 218 3. The y-globin Loci 220 4. The E-Globin Locus 221 5. The a-globin Loci 221 6. The ~-Globin Locus 223 B. New Globin-Gene Mutations 224 C. Acquired (Non-genetic) Thalassemias 226 D. Linkage Relationships Involving Polymorphic Sites in the Regions of the Globin Genes 227 1. Restriction Fragment Length Polymorphisms (RFLPs) in the ~-Globin Gene Cluster 228 2. Linkage Relationships of ~-Globin Gene Restriction Fragment Length Polymorphisms 230 3. Polymorphisms Within the ~-Globin Gene 232 4. Haplotype Associations with ~ Thalassemia 233 8. The Geographic Distribution of Globin Gene Variation 237 A. Distribution of the Hemoglobin Variants and Thalassemias 237 B. The Malaria Hypothesis 239 1. Geographic and Epidemiologic Evidence in Support of the Malaria Hypothesis 240 2. Experimental Evidence Related to Malarial Parasite Infectivity 243 C. Molecular Approaches to the Study of Genetic Diversity of the Globin Gene Alleles 245 1. Origins of the ~E-Globin Gene 245 2. The Origins of the ~s-globin Gene 247 3. Other Globin Mutations Associated with Multiple Haplotypes 249 9. Laboratory Identification, Screening, Education, and Counseling for Abnormal Hemoglobins and Thalassemias 251 A. The Laboratory Identification of Abnormal Hemoglobins and Thalassemias 251
XIV Contents 1. Blood Count Measurements 251 2. Electrophoretic Methods 252 a) Hemoglobin Electrophoresis at Alkaline ph 252 b) Citrate Agar Gel Electrophoresis 253 c) Globin Chain Electrophoresis 255 d) Measurement of the Electrophoretic Mobility of Hemoglobins and Globin Chains 255 e) Isoelectric Focusing 255 3. Other Methods for Abnormal Hemoglobin Characterization 257 a) Tests for Sickle Hemoglobin 257 b) Testing for Hemoglobin Functional Abnormalities and Instability 258 4. The Quantitative Estimation of Hemoglobins 258 5. Structural Characterization of Abnormal Hemoglobins 260 B. Screening for Abnormal Hemoglobins and Thalassemias 260 1. Screening to Determine the Variety and Frequency of Abnormal Globin Genes 261 2. Newborn Screening 262 3. Screening for Abnormal Hemoglobins Prior to Surgery or Childbirth 263 4. Screening of Volunteer Adults 263 a) Approaches to Education and Screening 263 b) Genetic Counseling 266 C. Antenatal Diagnosis 267 1. Diagnostic Methods Utilizing Fetal Blood 268 a) Fetal Blood Sampling 268 b) Analysis of Fetal Blood 269 2. Methods Which Utilize Fetal DNA 271 a) Fetal DNA Sampling 271 b) Fetal DNA Analysis 271 3. The Impact of Programs for Antenatal Diagnosis 276 10. Approaches to the Treatment of the Hemoglobin Disorders 277 A. Current Forms of Treatment for Patients with Hemoglobin Disorders 277 1. Transfusion Therapy 277 2. Other Therapy for the Management of Patients with Sickle Cell Disease and Thalassemia 279 B. New Directions in Therapy 280 1. Anti-sickling Therapy 280
Contents xv 2. Bone Marrow Transplantation 283 3. Chemotherapy for the Stimulation of Fetal Hemoglobin Synthesis 284 4. Gene Therapy 287 Appendix 289 Table A-I. The a-globin Gene Mutations 292 Table A-2. The ~-Globin Gene Mutations 308 Table A-3. The a-globin Gene Mutations 342 Table A-4. The Gy-Globin Gene Mutations 344 Table A-5. The Ay-Globin Gene Mutations 346 Table A-6. The Fusion Gene Mutations 348 References 351 Subject Index 437