MLAB 1415:Hematology Keri Brophy-Martinez Chapter 10: The Hemoglobinopathies Part Two
Hemoglobin C Disease
Introduction Amino acid substitution of lysine for glutamic acid at sixth position of Beta chain (α2β26Glu-Lys) Is homozygous CC Chronic hemolytic anemia with associated splenomegaly and abdominal discomfort
Laboratory Findings: Hb C Disease Mild to moderate anemia (8-12 g/dL) Retic count 4-8% (slightly increased) Electrophoresis Most hemoglobin is HbC no HbA present may or may not have increase in Hb F.
Peripheral Smear Numerous target cells, few microspherocytes, schistocytes, and folded cells May see hexagonal or rod-shaped crystals ("bar of gold”). Usually intracellular. Are elongated with blunt ends and parallel sides.
Hemoglobin C Trait (AC) No symptoms – no anemia. Target cells frequent finding.
Treatment for Hb C Splenectomy may be beneficial for symptomatic CC homozygous persons. AC heterozygous persons are usually asymptomatic, so no treatment required.
Hemoglobin SC Disease HbS gene is inherited from one parent and HbC gene is inherited from the other parent so both β- chains are abnormal Splenomegaly Patients can develop vaso-occlusive crisis
Peripheral Smear target cells folded red cells occasional glove- shaped intracellular crystals.
Hemoglobin E Disease
Hb E Disease β chain variant – lysine substituted for glutamic acid in 26th position in beta chain (α2β226Glu-Lys) Heterozygous and homozygous forms. Frequently occurs with Beta thalassemia No clinical symptoms
Laboratory Findings: Hb E Disease Similar to Hb D Mild, microcytic, hypochromic hemolytic anemia Many target cells Electrophoresis shows E band. Normal Hb F, no Hb A May protect against malaria
Unstable Hemoglobin Variants
Overview Unstable hemoglobins are hemoglobin variants in which amino acid substitutions or deletions have weakened the binding forces that maintain the structure of the molecule. Instability may cause Hb to denature and precipitate in the red cells as Heinz bodies.
Overview con’t Most inherited as autosomal dominant disorders. When anemia is present, degree of hemolysis varies considerably: Most have mild compensated anemia with mild reticulocytosis Some have severe, chronic hemolysis with splenomegaly and jaundice. Hb electrophoresis usually not very helpful in diagnosis.
Hemoglobin Variants with Altered Oxygen Affinity
Methemoglobinemia (Hemoglobin M)
Overview HbM contains ferric iron (Fe3+); Can’t carry oxygen and results in cyanosis. Three causes of methemoglobinemia: Methemoglobin reductase system Overwhelmed Deficient Molecule is resistant to methemoglobin reductase
Hb M 5 variants of Hb M which result from single amino acid substitution in the globin chain that stabilizes iron in the ferric form. Patients have cyanosis, but are otherwise asymptomatic and no treatment is given.
Laboratory Findings in Hb M Blood is chocolate brown. Mild hemolytic anemia. Heinz bodies. M band on electrophoresis.
Hemoglobins with Increased Oxygen Affinity Decreased delivery of oxygen to tissues. Hb values from normal to 20 g/dL. Leukocytes and platelets normal. Normal life span. No treatment. Often results in polycythemia.
Hemoglobins with Decreased Oxygen Affinity Increased release of oxygen to tissues. Patient may become anemic.
Referenes Harmening, D. M. (2009). Clinical Hematology and Fundamentals of hemostasis (5th ed.). Philadelphia, PA: F.A. Davis Company. McKenzie, S. B. (2010). Clinical Laboratory Hematology (2nd ed.). Upper Saddle River, NJ: Pearson Education, Inc. Rodak, B. F. (2002). Hematology Clinical Principles and Applications (3rd ed.). St. Louis: Saunders Elsevier.