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CR 2 > Haemoglobinopathies > Flashcards

Haemoglobinopathies Flashcards

1
Q

What chains make up adult haemoglobin?

What is it also known as?

A

2 alpha and 2 beta

Haemoglobin A

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2
Q

Where are the gene(s) for alpha subunit found

A

Chromosome 16

2 genes on each chromosome so 4 altogether

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3
Q

Where are the gene(s) for beta subunit found?

A

5 genes for beta subunit on chromosome 11

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4
Q

Name the 5 genes that can produce beta chain (5’ to 3’ direction)

A 
Epsilon
gamma A
gamma G
delta
beta
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5
Q

Is adult or foetal haemoglobin better at binding oxygen?

A

Foetal

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6
Q

What is the first form of haemoglobin formed in the embryonic yolk sac

A

Hb Gower-1, also called Zeta 2 Epsilon 2

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7
Q

What haemoglobin is made after week 6 of gestation

A

HbF (foetal haemoglobin)

Alpha 2 gamma 2

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8
Q

Where in the foetus is HbF made?

A

Liver and spleen

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9
Q

Does HbA, HbF or Hb Gower-1 have higher affinity?

A

H Gower-1

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10
Q

When does HbA start to replace HbF

A

3-6 months after birth

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11
Q

What is HbA2

A

alpha 2 delta 2

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12
Q

What % of each haemoglobin type are present in adult

A

96-97% HbA
2-3.5% HbA2
<1% HbF

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13
Q

What % of each haemoglobin types are found in neonate

A

10% HbA
<1% HbA2
90% Hbf

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14
Q

Define thalassaemia

A

Genetic defect resulting in inadequate quantities of one of the haemoglobin subunits

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15
Q

What is alpha thalassaemia

A

Results when one or more alpha genes of chromosome 16 is deleted or faulty

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16
Q

What is beta thalassaemia

A

Results when there is a point mutation of chromosome 11

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17
Q

When does alpha thalassaemia manifest

A

Immediately at birth

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18
Q

What happens if one alpha gene is defective

A

Alpha thalassaemia minima
Minimal effect on synthesis
Silent carriers

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19
Q

What happens if two alpha genes are defective?

A

Alpha thalassaemia minor
Mild microcytic anaemia
Can be mistaken for iron deficiency anaemia

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20
Q

What happens if three alpha genes are defective?

A

Haemoglobin H disease
2 unstable haemoglobins present in blood: Hb Barts (y4) and haemoglobin H (beta 4)
Microcytic hypochromic anaemia

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21
Q

What happens if four alpha genes are defective

A

Foetus can’t live outside uterus
Many stillborn, rest die after birth
Circulating haemoglobin is barts- tetrameric gamma chains

22
Q

How is beta thalassaemia inhertited

A

Autosomal recessive

23
Q

What are the 2 main genotypes of beta thalassaemia

A

Heterozygous (beta thalassaemia minor)

Homozygous (major/ Cooleys anaemia)

24
Q

When does beta thalassaemia manifest

A

Several months after bith when switch from gamma to beta chains begins

25
Q

Describe the pathological effects of beta thalassaemia

A

Excess alpha globins produced which are unstable and cause intra-medullary destruction of developing erythroblasts, erythroid hyperplasia and ineffective erythropoiesis

26
Q

How does HbF levels present in beta thalassaemia major

A

High

27
Q

Effects of untreated beta thalassemia major (5)

A
  • Hypochromic, microcytic anaemia
  • Bone marrow expansion
  • Bone deformity
  • Splenomegaly
  • Failure to thrive by 6 months, death aged 3-4
28
Q

Usual treatments for thalassamia major

A

Regular transfusions with iron chelating therapy to prevent overload
Bone marrow transplant
HbF modulating treatments

29
Q

What do iron chelating compounds do

A

Bind free iron and prevent Fenton reaction

30
Q

What is the fenton reaction and what does it cause?

A

Free iron reacts with hydrogen peroxide producing free radicals
Responsible for cirrhosis, diabetes, glandular synfunction

31
Q

Name an oral iron chelation therapy

A

Deferiprone

32
Q

Side effects of desferoxamine

A

Toxicity- diarrhoea, vomiting, fever, hearing and eye probs

33
Q

Side effects of deferasirox

A

GI bleeding, kidney and liver failure

34
Q

What is problem with having sickle shaped red cells?

A

Can block capillaries, restrict blood flow to organ and cause ischaemia, pain and organ damage

35
Q

Signs of sickle cell disease

A

Haemolytic anaemia (Hb 6-8)
Microvascular occlusion
Large vessel damage

36
Q

What mutation occurs in sickle cell anaemia

What does this produce?

A

GAG–> GTG
Glutamic acid–> valine
Abnormal beta chain

37
Q

What is the haemoglobin in sickle cell called

A

Haemoglobin S

alpha 2 beta S 2

38
Q

How does survival time differ in sickle cells

A

It is decreased

39
Q

4 major clinical consequences of sickle cell disease

A
  • Anaemia
  • Increased infection risk
  • Vaso-occlusive crises
  • Chronic tissue damage
40
Q

How can sickle cell be managed

A 
Analgesics for painful crises
Transfusion
Hyroxyurea increases HbF
Bone marrow transplant
Infection prophylaxis
41
Q

How can couples be screened for sickle cell

A

Simple blood analysis (full blood count and haemoglobinopathy screen)

42
Q

When is the highest risk time for sickle cell complication

A

6 months- 2 years

43
Q

How is neonatal screening carried out

A

Heel prick

Implemented in UK since 2006

44
Q

What is haemoglobin C?

A

Mutation causing abnormal Beta subunit
Reduced plasticity and flexibility–> haemolysis
Homo- mild haemolytic anaemia

45
Q

What is haemoglobin E?

A

Single point mutation in Beta

3-6 months fetal haemoglobin disappears, HbE increases mild beta thalassamia

46
Q

Which gene is switched off after 6 weeks of gestation

A

Zeta gene

47
Q

Where is the first form of haemoglobin produced

A

Embryonic solk sac

48
Q

Where is HbF produced

A

Liver/ spleen

49
Q

What variants of Gower haemoglobin can occur in the early weeks

A
  • Gower 2 alpha episilon 2

Portland

50
Q

How does beta thalassaemia major lead to microcytic anaemia

A

Bodys inability to construct beta-globins–> underproduction of haemoglobin A.
Reduction in HBA available to fill red blood cells leads to microcytic anaemia

51
Q

Describe the blood results of a heterozygous character of beta thalassaemia

A
  • Mildly low Hb
  • Low MCV
  • Normal HbA
  • High HBA2
  • Normal HbF
52
Q

How may HbS behave in deoxygenated blood

A

Precipitate or cystallise, distorting the cells and making them fragile and easily destroyed

CR 2 (33 decks)

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