Haemoglobinopathies Flashcards
Describe the structure of adult haemoglobin (Hb A)
There are 4 global subunits (two alpha and two beta) which an iron-containing haem group
Describe the alpha globin gene cluster for haemoglobin
On chromosome 16 there are two genes that code for the alpha subunit of haemoglobin (Therefore there are 4 copies in total, 2 maternal and 2 paternal) but there is also a zeta gene that can produce the zeta subunit instead of the alpha subunit
Describe the beta globin gene cluster for haemoglobin
On chromosome 11 there is a gene that codes for the beta globin chain, but also the epsilon gene, delta gene and two gamma genes that can produce these subunits instead of the beta subunit
Where is the gene for the zeta globin subunit found?
Chromosome 16
Where is the gene for the alpha globin subunit found?
Two copies on chromosome 16
What is the structure of haemoglobin Gower 1 (embryonic haemoglobin)?
Consist of two zeta and two epsilon subunits
What is the advantage of Hb Gower 1 in the first stages of embryonic development?
It has a very high affinity for oxygen which allows greater uptake from the placenta
Where is embryonic haemoglobin (Hb Gower 1) produced?
Embryonic yolk sac until about 6 weeks gestation
What is the structure of foetal haemoglobin (Hb F)?
There are two alpha subunits and two gamma subunits
Where is foetal haemoglobin (Hb F) produced?
Spleen and liver
What is the advantage of haemoglobin F for the foetus?
It has a greater affinity for oxygen than maternal haemoglobin which allows it to take up oxygen from placental blood
What is the structure of adult haemoglobin (Hb A)?
Two alpha and two beta subunits
What is the structure of adult haemoglobin 2 (Hb A2)?
Two delta subunits and two alpha subunits
What is meant by thalassaemia?
A condition that is caused by inadequate quantities of one or other of the subunits that make up adult haemoglobin
What is alpha thalassaemia?
This occurs when one or more of the alpha genes on chromosome 16 are defective or faulty
What is beta thalassaemia?
This occurs when there is a point mutation on chromosome 11 which interferes with beta subunit production by varying amounts
What does the severity of alpha thalassaemia depend on?
The number of gene allies that are defective or missing