Chapter 099. Disorders of Hemoglobin (Part 12) The homozygous state for the α-thalassemia-1 cis deletion (hydrops fetalis) causes total absence of α-globin synthesis. No physiologically useful hemoglobin is produced beyond the embryonic stage. Excess γ-globin forms tetramers called Hb[r]
Chapter 099. Disorders of Hemoglobin (Part 1) Harrison's Internal Medicine > Chapter 99. Disorders of Hemoglobin Disorders of Hemoglobin: Introduction Hemoglobin is critical for normal oxygen delivery to tissues; it is also present in erythrocytes in such high concentrations that it c[r]
Chapter 099. Disorders of Hemoglobin (Part 8) Acute chest syndrome is a medical emergency that may require management in an intensive care unit. Hydration should be monitored carefully to avoid the development of pulmonary edema, and oxygen therapy should be especially vigorous for protectio[r]
Chapter 099. Disorders of Hemoglobin (Part 14) Deferasirox is a promising oral iron-chelating agent. Single daily doses of 20 or 30 mg deferasirox produced reductions in liver iron concentration comparable to desferoxamine in chronically transfused adult and pediatric patients. Deferasirox p[r]
Chapter 099. Disorders of Hemoglobin (Part 13) Hemoglobin E HbE (i.e., α2β226Glu -> Lys) is extremely common in Cambodia, Thailand, and Vietnam. The gene has become far more prevalent in the United States as a result of immigration of Asian persons, especially in California, where HbE[r]
Chapter 099. Disorders of Hemoglobin (Part 10) Low-affinity hemoglobins should be considered in patients with cyanosis or a low hematocrit with no other reason apparent after thorough evaluation. The P50 test confirms the diagnosis. Counseling and reassurance are the interventions of choice.[r]
Chapter 099. Disorders of Hemoglobin (Part 9) Unstable hemoglobins occur sporadically, often by spontaneous new mutations. Heterozygotes are often symptomatic because a significant Heinz body burden can develop even when the unstable variant accounts for a portion of the total hemoglobin. Sy[r]
Chapter 099. Disorders of Hemoglobin (Part 11) Severity is highly variable. Known modulating factors are those that ameliorate the burden of unpaired α-globin inclusions. Alleles associated with milder synthetic defects and co-inheritance of α-thalassemia trait reduce clinical severity by re[r]
Chapter 099. Disorders of Hemoglobin (Part 7) Clinical Manifestations of Sickle Cell Trait Sickle cell trait is usually asymptomatic. Anemia and painful crises are exceedingly rare. An uncommon but highly distinctive symptom is painless hematuria often occurring in adolescent males, probably[r]
Chapter 099. Disorders of Hemoglobin (Part 2) Figure 99-2 Hemoglobin-oxygen dissociation curve. The hemoglobin tetramer can bind up to four molecules of oxygen in the iron-containing sites of the heme molecules. As oxygen is bound, 2,3-BPG and CO2 are expelled. Salt bridges are broken, and[r]
Chapter 099. Disorders of Hemoglobin (Part 5) Sickle Cell Syndromes The sickle cell syndromes are caused by a mutation in the β-globin gene that changes the sixth amino acid from glutamic acid to valine. HbS (α2β26 Glu→Va1) polymerizes reversibly when deoxygenated to form a gelatinous networ[r]
Chapter 099. Disorders of Hemoglobin (Part 4) Epidemiology Hemoglobinopathies are especially common in areas in which malaria is endemic. This clustering of hemoglobinopathies is assumed to reflect a selective survival advantage for the abnormal RBC, which presumably provide a less hospitabl[r]
Chapter 099. Disorders of Hemoglobin (Part 6) Clinical Manifestations of Sickle Cell Anemia Most patients with sickling syndromes suffer from hemolytic anemia, with hematocrits from 15–30%, and significant reticulocytosis. Anemia was once thought to exert protective effects against vasoocclu[r]
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 produc[r]
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