TAILIEUCHUNG - Chapter 099. Disorders of Hemoglobin (Part 3)

Classes There are five major classes of hemoglobinopathies (Table 99-1). Structural hemoglobinopathies occur when mutations alter the amino acid sequence of a globin chain, altering the physiologic properties of the variant hemoglobins and producing the characteristic clinical abnormalities. The most clinically relevant variant hemoglobins polymerize abnormally, as in sickle cell anemia, or exhibit altered solubility or oxygen-binding affinity. Thalassemia syndromes arise from mutations that impair production or translation of globin mRNA, leading to deficient globin chain biosynthesis. Clinical abnormalities are attributable to the inadequate supply of hemoglobin and the imbalances in the production of individual globin chains, leading to premature. | Chapter 099. Disorders of Hemoglobin Part 3 Classes There are five major classes of hemoglobinopathies Table 99-1 . Structural hemoglobinopathies occur when mutations alter the amino acid sequence of a globin chain altering the physiologic properties of the variant hemoglobins and producing the characteristic clinical abnormalities. The most clinically relevant variant hemoglobins polymerize abnormally as in sickle cell anemia or exhibit altered solubility or oxygen-binding affinity. Thalassemia syndromes arise from mutations that impair production or translation of globin mRNA leading to deficient globin chain biosynthesis. Clinical abnormalities are attributable to the inadequate supply of hemoglobin and the imbalances in the production of individual globin chains leading to premature destruction of erythroblasts and RBC. Thalassemic hemoglobin variants combine features of thalassemia . abnormal globin biosynthesis and of structural hemoglobinopathies . an abnormal amino acid sequence . Hereditary persistence of fetal hemoglobin HPFH is characterized by synthesis of high levels of fetal hemoglobin in adult life. Acquired hemoglobinopathies include modifications of the hemoglobin molecule by toxins . acquired methemoglobinemia and abnormal hemoglobin synthesis . high levels of HbF production in preleukemia and a-thalassemia in myeloproliferative disorders . Table 99-1 Classification of Hemoglobinopathies I. Structural hemoglobinopathies hemoglobins with altered amino acid sequences that result in deranged function or altered physical or chemical properties A. Abnormal hemoglobin polymerization HbS hemoglobin sickling B. Altered O2 affinity 1. High affinity polycythemia 2. Low affinity cyanosis pseudoanemia C. Hemoglobins that oxidize readily 1. Unstable hemoglobins hemolytic anemia jaundice 2. M hemoglobins methemoglobinemia cyanosis II. Thalassemias defective biosynthesis of globin chains A. a-Thalassemias B. .

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