Hemoglobin abnormalities

Hemoglobin abnormalities

Updated: 07/11/2024

© Jun Wang, MD, PhD

 

Hemoglobin

  • Oxygen binding protein of red blood cells
  • A tetramer, each containing an iron atom bound to a heme group
  • Normally consists of four polypeptide subunits
  • Most common 2 a and 2 b chains
  • Measured as a part of CBC

Commonly seen hemoglobin variants and their levels

  • Hb A1: 2 a and 2 b, ≥ 95 % (95% to 98 %).
  • Hb A2: 2 a and 2 d, 1.5% to 3.7 %
  • Hb F: 2 a and 2 g, ≤ 2 % (0.8 to 2 %).
  • Hb S: point mutation of b, absent
  • Hb C: point mutation of b, absent
  • Hb E: point mutation of b, absent
  • Newborn Hb F = 50% to 80%

o   <6 months = <8 %

o   >6 months = 1% to 2 %

Hereditary hemoglobin disorders

  • Associated with abnormal assembly of hemoglobin
  • Two major categories:

o   Hemoglobinopathies

§  Mutations of hemoglobin genes

§  Abnormal hemoglobin structure

§  Commonly β-chain mutations: HbS, HbE, HbC. 

o   Thalassemia

§  Defects of hemoglobin production

§  Various abnormalities affecting HB synthesis, from gene expression to posttranslational assembly

§  Two main types: a- and β-thalassemia

  • Concurrent hemoglobin abnormalities may occur

Diagnosis

Hemoglobin abnormalities to be discussed

o   a thalassemia

o   b thalassemia

  • Hemoglobin C disease

o   Substitution of lysine for glutamate in the b-globin chain

o   Same point as the substitution in HbS codon 6

o   Forms rhomboidal crystals

o   Homozygous:  mild hemolytic anemia and possible splenomegaly

o   Generally benign condition

  • Hemoglobin E disease

o   Most common Hb variant in SE Asia

o   Substitution of glutamic acid by lysine at codon 26 of the b-globin gene

o   Mild microcytic hypochromic anemia if homozygous

o   May have concurrent sickle cell mutation

o   Mutations affecting b globin expression may cause presentations similar to thalassemia

o   May have target cells

 

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Anemia

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