PBL 9 - Thalassaemia Flashcards

1
Q

How does the subunit structure of normal adult haemoglobin differ from that of fetal haemoglobin? (2 marks)

A

Normal adult haemoglobin consists of two alpha (1/2 mark) and two beta (1/2 mark) subunits (chains) . Fetal haemoglobin consists of two alpha (1/2 mark) and two gamma subunits (1/2 mark).

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2
Q

What abnormality occurs specifically in alpha thalassaemia? (1 mark). What are the different degrees of this disease, and describe briefly the signs corresponding to each degree of severity. (2 marks)

A

In Alpha thalassaemia there is reduced synthesis (1/2 mark) of the alpha subunits of haemoglobin (1/2 mark).

There are usually four copies of the gene to produce alpha chain haemoglobin (1/2 mark). If all four copies are missing this is incompatible with life and leads to in-utero death (1/2 mark). Three copies missing leads to severe microcytic anaemia (1/2 mark). Loss of one or two genes does not normally lead to any symptoms (1/2 mark).

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3
Q

What is the main abnormality that would be detected in a blood test from patients with beta thalassaemia major (1 mark)

A

Microcytic anaemia

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4
Q
  1. What is the major form of haemoglobin in patients with beta thalassaemia major (1 mark)
A

Fetal Haemoglobin (HbF)

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5
Q
  1. Explain briefly why Kadeer Ahmed has a protruberant abdomen (1 mark)
A

There is enlargement of the liver and spleen (1/2 mark) as a result of excessive red cell destruction (1/2 mark) and extramedullary haemopoiesis (1/2 mark) (any two half marks)

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6
Q

Name two main forms of treatment suitable for Kadeer (2 marks)

A

Regular blood transfusions (1/2 mark) with iron chelation to prevent iron overload (1/2 mark)
Bone marrow transplant (1 mark)

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7
Q

Where is blood cell production in the fetus, newborn and adult? (3)

A

o Before birth:
= Mesoblastic stage - At 3rd week: Yolk sac +mesothelial layers of the placenta (HbGower1)
=Hepatic stage - At 6 weeks – Liver & Spleen (HbF)
=Myeloid stage- 3rd month onwards - the bone marrow
o After birth:
=Age up to 5 years : The bone marrow in all bones (HbA)
= Age 5 to 20-25 years : Marrow of the long bones
= Age 25+ years: marrow of the membranous bones

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8
Q

What is the difference between the structure of embryonic and fetal hb? (2)

A

Fetal Hb - HbF - A2Y2

fetal - Hb Gower 1 - Z2E2

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9
Q

What is the percentage of HbA, HbF and HbA2 in adult blood?

A

o HbA – 10% in neonates, 96-97% in adults
o HbA2 - <1% in neonates, 2-2.5% in adults
o HbF – 90% in neonates, <1% in adults

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10
Q

What chromosome do B thalassaemia mutations occur on? (1)

A

e within the gene complex

itself or in promoter or enhancer regions on chromosome 11.

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11
Q

What are the two genotypes of B thalassaemia ? (2)

A

heterozygous beta thalassaemia trait (minor) and

homozygous beta thalassaemia (thalassaemia major or intermedia).

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12
Q

Why are iron chelators given and give an example? (1)

A

E.g Desferioxamine
bind to iron in blood
Prevents the Fenton reaction occurring (hydroxyl radicals form) which can cause cirrhosis, growth retardation, heart failure, diabetes

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13
Q

Why might genetic counselling be necessary, what would they need to discuss? (1)

A
  • Pregnant woman with Hb abnormality – test partner
  • Both have abnormality – risk of defect in offspring

Discuss - foetus affect, termination offered

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14
Q

How can prenatal diagnosis of thalassaemia be done? (1)

A

DNA (chorionic villous or amniotic fluid) or fetal blood

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15
Q

Normal structure and function of haemoglobin

A

4 polypeptide chains with a haem group

Each haem has 1 atom of ferrous iron that combines with 4x oxygen

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16
Q

What chromosome is the gene for alpha globin on

A

Ch 16

4x genes for alpha + zeta

17
Q

What chromosome is the gene for beta globin on

A

Ch 11

5x genes for beta

18
Q

Structure of embryonic, fetus, adult hb

A

Embryonic Hb - Hb Gower 1 – Z2E2
• Fetus Hb – HbF – A2Y2
• Adult Hb – HbA – A2B2 and HbA2 – A2D2

19
Q

When do babies switch to adult hb

A

3-6 months after birth

the gamma is replaced by beta

20
Q

What is thalassaemia

A

Reduction or absence globin chain production

21
Q

Alpha thalassaemia

A

Deletion on one or more alpha genes on ch 16

22
Q

What are the different types of alpha thalassaemia

A

Alpha thalassaemia minima
Alpha thalassaemia minor
Haemoglobin H
Alpha thalassaemia major

23
Q

What is alpha thalassaemia minima

A

One alpha gene defective
Asymptomatic as 3 alpha globin chains are enough
Silent carriers

24
Q

What is alpha thalassaemia minor

A

Two alpha genes defective

Mild microcytic hypochromatic anaemia

25
Q

Haemoglobin H

A

3 alpha genes defective
2 unstable haemoglobins present in the blood - Hb Barts and Hb H
Severe microcytic hypochromatic anaemia
Higher affinity for oxygen- poor release in tissues

26
Q

What is hb barts and hb H

A

Hb Barts - G4

Gb H - B4

27
Q

Alpha thalassaemia major

A

4 alpha genes defective
Foetus cannot live outside of uterus (stillborn)
Hb that is present is all hb barts

28
Q

What sort of inheritance is beta thalassaemia

A

Autosomal recessive

29
Q

What is beta thalassaemia

A

point mutation on genes on ch 11 in hb b gene

30
Q

When does beta thalassaemia manifest

A

When switch from gamma to beta chain after birth

31
Q

Beta thalassaemia minor

A

Heterozygous - carrier state

Asymptomatic

32
Q

Beta thalassaemia intermedia

A

Moderate anaemia

Still can make some beta chains

33
Q

Beta thalassaemia major

A

Lack of beta haemoglobin
Severe microcytic anaemia
Cooley’s

34
Q

Signs and symptoms of B thalassaemia

A

 Bone deformities – extramedullary haematopoiesis
 Jaundice due to haemolytic anaemia
 Abdominal distention due to hepatosplenomegaly
 Failure to thrive from 6 months of age
 Heart failure and death by age 3-4

35
Q

What would you see in investigations of B thalassaemia

A

 Full blood count – Microcytic anaemia, reticulocytosis
 Haemoglobin electrophoresis – HbA very reduced or absent, HbA2 slightly increases, HbF increased
 Blood film – Hypochromatic, microcytic rbc and reticulocytes present
 Other tests – Increased bilirubin, increased lactate dehydrogenase
 Difference between hetero and homozygote is that homozygote will have very reduced/absent HbA, increased HbF and very reduced Hb

36
Q

How do you treat beta thalassaemia

A

1) Blood transfusions 2-4 per week
2) + Iron chelators e.g desferioxamine preventing fenton reaction
3) Allogenic bone marrow transplant
4) Splenectomy

37
Q

Why jaundice in scenario

A

Raised serum bilirubin and LDH due to increased ineffective erythropoiesis and haemolysis, bilirubin is a breakdown product of haemoglobin and LDH is released from damaged erythroblasts and red cells

38
Q

Why was the liver and spleen enlarged

A

excessive red cell destruction and extramedullary haemopoiesis

39
Q

Function of 2,3 DPG

A

When O2 starts to be unloaded from oxyhaemoglobin the beta chains separate permitting entry of the metabolite 2,3-diphosphoglycerate (2,3-DPG) this in turn reduces the affinity of the whole molecule for O2. This entry of 2,3 DPG is responsible for the sigmoid form of the haemoglobin O2 dissociation curve. The normal position of the curve depends on the concentration of 2,3-DPG, H+ ions and CO2 in the red cell and on the structure of the haemoglobin molecule