Sickle Cell Anaemia Flashcards
1
Q
What are Haemoglobinopathy?
A
- arise from genetic mutation in globin gene
- different type/altered amount of haemoglobin synthesised
- leads to anaemia
- sickle cell & thalassaemias are examples
- almost always inherited
2
Q
Describe Sickle Cell Anaemia
A
- mutation in beta globin chain
- results from a monobasic change in DNA sequence, and therefore a single amino acid change in the peptide chain
3
Q
Describe the sickle cell anaemia genotype
A
- classified by number & type of genes that are abnormal
- if both genes carry the sickle mutation then an individual is said to be homozygous HbSS
- an individual with only one mutated gene is heterozygous - inheritance pattern ‘carrier’ = HbAS
4
Q
Describe HbS Point Mutation
A
- subsituted amino acid at position 6
- this gives the beta globin molecules, and so the whole haemoglobin molecule is a different shape & hence a reduced ability to carry oxygen
- carries oxygen poorly
5
Q
Describe Right Shift
A
- HbS gives up O2 more readily than HbA
- impacts on tissue perfusion
6
Q
Describe Red Cell ‘Sickling’
A
- low oxygen tension
- dehydration
- fever
- initially reversible by re-oxygenation
- irreversible sickling occurs after repetive cycles of oxygenation & deoxygenation
7
Q
Why does HbS become insoluble ?
A
- HbS is soluble, when fully oxygenated
- deoxygenation triggers polymeraisation of Hbs into long rigid chains - insoluble
- distort red cell shape - flow through capillaries affected
8
Q
What is Vaso-occlusion?
A
- sickled cells obstruct blood flow through capillary blood
- reduced tissue perfusion downstream of infarct
- sickled cells = reduced deformability & increased adhesion
9
Q
Describe clinical features of sickle cell anaemia
A
- Sickle crisis = from 9 months onwards, severe & debilitating pain
- vast-occlusion initiates tissue hypoxia -> pain
10
Q
What are some examples of treatments ?
A
Transfusions, prophylaxis, hydroxyurea & bone marrow transplant
11
Q
Describe how transfusions treat sickle cell anaemia
A
- relieves anaemia
- mature HbA red cells introduced to patients circulation
- improves oxygen transport
- buffers ‘right shift’ as HbS cells diluted with transfused HbA cells
12
Q
Describe how Hydroxyurea treat sickle cell anaemia
A
- induced HbF production
- offers some protection against sickle crisis & chronic complications
13
Q
Describe how Prophylaxis treat sickle cell anaemia
A
- pneumococcal immunisation & antibiotics prevent development of common illness
- prevents fever as this can trigger sickle crisis
14
Q
Define HbSS
A
Sickle Cell anaemia
15
Q
Define HbAS
A
- Sickle ‘trait’ -> some mild feature of sickle cell anaemia & carrier of HbS mutation
16
Q
Define HbSC
A
- Variable disease severity
- different point mutations in beta globin genes
- Hbc is lysine at position 6
17
Q
Define HbS beta thalassaemia
A
- compound phenotype
- feautres of both haemoglobinopathies
