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Y3 HAEMATOLOGY > Haemoglobinopathy > Flashcards

Haemoglobinopathy Flashcards

1
Q

Describe the structure of haemoglobin

A

Tetramer
4 globin chains
One haem group attached to each globin chain

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2
Q

What are the 3 main forms of haemoglobin?

A

HbA: (2-alpha, 2-beta)
HbA2: (2-alpha, 2-delta)
HbF: (2-alpha, 2-gamma)

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3
Q

The genes making the alpha protein for haemoglobin are located on which chromosome? How many alpha genes are on each chromosome?

A

Chromosome 16
2 alpha genes per chromosome
4 per cell

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4
Q

The genes making the beta protein for haemoglobin are located on which chromosome? How many beta genes are on each chromosome?

A

Chromosome 11
1 beta gene per chromosome
2 per cell

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5
Q

Which type of haemoglobin - HbA, HbA2 or HbF - is found in a foetus?

A

HbF

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6
Q

When does foetal haemoglobin typically reach adult level following birth?

A

6-12 months

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7
Q

What are haemoglobinopathies?

A

Hereditary conditions affecting globin chain synthesis

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8
Q

What inheritance pattern do haemoglobinopathies generally follow?

A

Autosomal recessive

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9
Q

What are the 2 main groups of haemoglobinopathies?

A

Thalassaemias

Structural variant

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10
Q

What is the problem in thalassaemias?

A

Decreased rate of globin chain synthesis, resulting in less haemoglobin (causes a microcytic hypochromic anaemia) and toxic accumulation of globin chains

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11
Q

What is the problem in structural variant haemoglobinopathy?

A

Normal production of structurally abnormal globin chains, resulting in variant haemoglobin

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12
Q

Alpha thalassaemia (affecting alpha-chain synthesis) results from deletion of how many - one or both - alpha genes from chromosome 16?

A

Either! Can arise due to deletion of one alpha gene or both alpha genes

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13
Q

What are the 3 classifications of alpha thalassaemia?

A

Trait: 1 or 2 genes missing
HbH: 1 alpha gene left
Bart’s hydrops fetalis: no alpha genes

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14
Q

Alpha thalassaemia trait is usually asymptomatic. True/False?

A

True

Mild anaemia and may be mistaken for iron deficiency

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15
Q

Describe the clinical features of HbH alpha thalassaemia

A 
Anaemia
Very low MCV
Splenomegaly
Jaundice
Growth retardation
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16
Q

What can be seen on special staining of red cells in HbH alpha thalassaemia?

A

Red cell inclusions (HbH bodies)

‘Golf ball’

17
Q

Describe the clinical features of Bart’s hydrops fetalis alpha thalassaemia

A 
Severe anaemia (can't make Hb)
Cardiac failure
Oedema
Growth retardation
Hepatosplenomegaly
Skeletal abnormality
Death in utero
18
Q

Beta thalassamia only affects beta chains, thus which type of haemoglobin production is affected?

A

Only affects HbA production

19
Q

What type of mutations are typical in alpha and beta thalassaemias respectively?

A

Alpha thalassaemia typically due to deletions

Beta thalassaemia typically due to point mutations

20
Q

What are the 3 classifications of beta thalassaemia?

A

Trait: no or 1 gene missing
Intermedia: 1 gene missing
Major: 2 genes missing

21
Q

What are the laboratory features of beta thalassaemia major?

A

Very low MCV
Microcytosis, hypochromia
Anisopoikilocytosis
Target cells

22
Q

Beta thalassaemia major is transfusion dependent. True/False?

A

True

23
Q

Severe thalassaemia can cause extramedullary haematopoiesis. What are the consequences of this?

A

Hepatosplenomegaly
Skeletal changes
Organ damage
Cord compression

24
Q

What becomes the main cause of mortality from transfusion treatment for beta thalassaemia major?

A

Iron overload

Causes endocrine dysfunction, cardiac and liver disease

25
Q

How can iron overload secondary to transfusion be managed?

A

250mg of iron per unit of red cells

Iron-chelating drug (desferrioxamine)

26
Q

What is the best method of diagnosing thalassaemia? What does it show?

A

High performance liquid chromatography (HPLC)

Quantifies Hb present and identifies abnormal Hb

27
Q

What is the pathophysiology of sickle cell disorder?

A

Point mutation in codon 6 of beta-globin gene, causing valine production instead of glutamine, altering the structure of Hb to produce HbS

HbS polymerises if exposed to low oxygen causing damage to the red cell membrane

28
Q

What is the genetic makeup of sickle-cell trait?

A

One normal beta gene, one abnormal beta gene

29
Q

Is sickle cell anaemia autosomal dominant or recessive?

A

Autosomal recessive

Requires 2 abnormal beta genes

30
Q

What is a sickle crisis?

A

Episodes of tissue infarction due to vascular occlusion by sickle cells causing severe pain

31
Q

List some precipitants of a sickle crisis

A 
Hypoxia
Dehydration
Infection
Cold exposure
Stress
Fatigue
32
Q

Outline treatment of a sickle crisis

A 
Opiate analgesia
Hydration
Rest
Oxygen
Antibiotic if infection
Red cell transfusion if severe
33
Q

What long-term treatment may be given for sickle cell disorder?

A

Penicillin and vaccination if hyposplenism
Folic acid (increase RBC turnover)
Hydroxycarbamide (induce HbF production)
Regular transfusion to prevent stroke

34
Q

How is alpha thalassaemia distinguished from iron deficiency anaemia?

A

Ferritin levels are normal

35
Q

What is HbH disease?

A

Excess B chains form tetramers that are unable to carry oxygen

36
Q

When does beta thalassaemia usually present?

A

6-24 months when fetal haemoglobin starts to fall and newborn is unable to produce HbA

37
Q

List major complications of long term sickle cell anaemia

A

Hypospleenism
Impaired growth
Risk of end organ damage

38
Q

Prescence of which Hb on HPLC is indicative of beta thal trait?

A

HBA2

39
Q

HPLC is normal in alpha thal trait. True/ False?

A

True

DNA testing needed to confirm

Y3 HAEMATOLOGY (16 decks)

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