Lecture 8.2: Haemoglobinopathies and Screening Flashcards
Normal Adult Haemoglobin: HbA
90%
α2β2
Normal Adult Haemoglobin: HbF
<2%
α2γ2
Normal Adult Haemoglobin: HbA2
2-5%
α2δ2
The Importance of Foetal Haemoglobin
HbF is the major haemoglobin in foetal blood
Higher binding affinity for O2 than HbA which allows transfer of O2 to foetal blood supply from the mother
Cannot bind 2,3 BPG so favours oxygen loading
Genetic Mechanisms of Haemoglobin Diseases: Quantitative
• Too little (or too much) globin chain synthesis
• Thalassaemia
Genetic Mechanisms of Haemoglobin Diseases: Qualitative
• Synthesis of abnormal gene product (structural variants)
• Sickle cell disease (and many others)
Thalassaemias
Autosomal Recessive
Decreased or absence of synthesis of one of the two polypeptide chains (α or β)
Results in reduced haemoglobin in red cells and anaemia
How are Thalassaemias Classified: Globin Chains
The thalassaemias are classified according to which chain of the globin molecule is affected
α thalassaemia- the production of α globin is deficient
β thalassaemia- the production of β globin is defective
How are Thalassaemias Classified: Severity
Thalassaemia major, intermedia and minor refer largely to disease severity
4 Types of Alpha Thalassaemia
Normal: genotype α,α/α,α (2 on each chromosome 16)
α+ Trait: 1 alpha deletion, asymptomatic, low MCV / MCHC, raised red cell count
Homozygous α+ trait: -Asymptomatic, low MCV / MCHC, raised RBC count
(borderline anaemia)
α0 Trait: Asymptomatic, low MCV / MCHC, raised red cell count
MCV
Mean Corpuscular Volume
Three main types of corpuscles (blood cells) in your blood–red blood cells, white blood cells, and platelets
An MCV blood test measures the average size of your red blood cells, also known as erythrocyteS
MCHC
Mean Corpuscular Haemoglobin Concentration
It is a measure of the concentration of haemoglobin in a given volume of packed red blood cell
