Haemoglobinopathies Flashcards
How are most haemoglobinopathies inherited?
AR
On which Ch are the a-globin genes located?
Ch 16
On which Ch are the B-globin genes located?
Ch 11
What are the a-globin genes?
ζ
a1
a2
What are pseudogenes?
Non-functional genes which are not transcribed
Includes φζ and φα on Ch 16, and φβ on Ch 11
What are the B-globin genes?
ε Gγ Aγ δ β
What is the difference between Gγ and Aγ?
Functionally identical (difference of 1 residue)
Where is Hb synthesised in the embryo and foetus?
Embryo: yolk sac
Foetus: liver and spleen
What are the 3 types of embryonic Hb?
ζ2ε2
ζ2γ2
a2ε2
What is the foetal form of Hb?
a2γ2
What is the normal types and proportions of Hb in the adult?
97.5% HbA
2% HbA2
0.5% HbF
NB: proportions may change in carriers or those with a haemoglobinopathy
What is the globin chain composition of HbA?
a2B2
What is the globin chain composition of HbA2?
a2δ2
In what order do the globin chains switch throughout development?
In order of physical location on Ch (proximal to LCR, to distal from LCR)
What is LCR?
Locus control region (for regulation of globin gene expression)
What are the 3 main types of haemoglobinopathies?
Thalassaemias
Structural variants
Hereditary persistence of foetal Hb (HPFH)
What is the basis of thalassaemias?
Decreased or absent synthesis of 1 or more globin chains
What is the basis of structural variants of Hb?
Altered globin polypeptide without altering rate of synthesis
How many Hb structural variants are there?
> 500
Give an example of a haemoglobinopathy which is the result of a Hb structural variant
Sickle cell disease
What is HPFH?
Clinically benign condition in which HbF continues to be produced in adulthood
Describe the distribution of a-thalassaemias
Global, but high in SE Asia
Describe the distribution of B-thalassaemias
Global, but high in Southern Europe, Middle Eastern, North African and SE Asian countries, as well as the Indian subcontinent