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
- Confirmed by hemoglobin electrophoresis or HPLC
Hemoglobin abnormalities to be discussed
- 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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