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Haematology > Haemoglobinopathies > Flashcards

Haemoglobinopathies Flashcards

1
Q

What are the major forms of haemaglobin?

A

HbA (2 alpha and 2 beta)
HbA2 (2 alpha and 2 delta)
HbF (2 alpha and 2 gamma)

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2
Q

What are the proportions of each form of haemaglobin in adults?

A 
HbA = 97% 
HbA2 = 2.5% 
HbF = 0-0.5%
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3
Q

What chromosome codes for alpha globin genes and how many are present?

A

Chromosome 16

2 alpha genes per chromosome (4 per cell)

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4
Q

What chromosome codes for beta globulin genes and how many are present?

A

Chromosome 11

One beta gene per chromosome (2 per cell)

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5
Q

At what point are adult levels of Hb reached in a child?

A

6-12 months - this is when beta chain problems will present

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6
Q

What are haemoglobinopathies?

A

Hereditary conditions affecting globin chain synthesis

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7
Q

What inheritance do haemoglobinopathies show?

A

AR

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8
Q

What are the 2 main groups of haemoglobinopathies?

A

Thalassaemias; decreased rate of globin chain synthesis

Structural haemaglobin variants; normal production of abnormal globin chain (variant haemaglobin e.g. HbS)

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9
Q

What are the different forms of thalassaemias?

A

Alpha

Beta

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10
Q

On FBC, how will thalassaemias present?

A

Microcytic, hypochromic anaemia with a normal ferritin

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11
Q

What are the consequences of thalassaemias?

A

Inadequate Hb production
Haemolysis
Ineffective erythropoiesis

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12
Q

What forms of Hb will be affected in alpha thalassaemia?

A

ALL forms; HbA, HbA2 and HbF

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13
Q

How are alpha thalassaemia’s classified?

A

Based on the number of alpha genes affected

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14
Q

What is alpha thal trait?

A

One or two alpha genes missing

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15
Q

What is HbH disease?

A

Only one alpha gene left out of 4

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16
Q

What is Hb Barts hydrops foetalis?

A

No functional alpha genes; tends to die in utero

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17
Q

Will people with alpha thalassaemia trait be symptomatic?

A

No; no treatment needed
Microcytic, hypochromic red cells with mild anaemia may be seen
Need to distinguish from iron deficiency (ferritin normal)

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18
Q

How will HbH disease present?

A

Anaemia with a very low MCV and MCH
Jaundice
Splenomegaly

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19
Q

What will HbH look like on a blood film?

A

Excess beta chains will form tetramers; HbH

Red cell inclusions of HbH can be seen with special stains

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20
Q

Does HbH disease require treatment?

A

May require transfusions

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21
Q

What is Hb Barts?

A

Tetramers of gamma Hb produced

22
Q

How can Hb Bart’s Hydrops Foetalis Syndrome be avoided?

A

Antenatal screening

23
Q

What are the clinical features of Hb Bart’s Hydrops Foetalis Syndrome?

A 
Profound anaemia 
Cardiac failure 
Growth retardation
Severe hepatosplenomegaly 
Skeletal and CV abnormalities
Almost all die in utero
May see nucleated red cells due to ineffective marrow funciton
24
Q

By what genetic mechanism is beta thalassaemia caused?

A

Point mutations
Reduced beta or absent beta chain production depending on mutation
Only beta chains and hence only HbA affected

25
Q

How is beta thalassaemia classified?

A

Clinical severity

26
Q

Describe beta thalassaemia trait?

A

Asymptomatic, no/mild anaemia, low MCV/ MCH

Raised HbA2

27
Q

What is the diagnostic test for beta thalassaemia?

A

Raised HbA2 (alpha and delta chained Hb)

28
Q

Describe beta thalassaemia intermedia?

A

Moderate severity requiring occasional transfusion (similar to HbH)

29
Q

Describe beta thalassaemia major?

A

Severe, lifelong transfusion dependency

30
Q

When will beta thal major present?

A

6-24 months as HbF fallls
Pallor, failure to thrive
Extramedullary haematopoiesis

31
Q

What will beta thal major show on Hb analysis?

A

Mainly HbF

No HbA

32
Q

What are the signs of extramedullary haematopoiesis?

A

Hepatosplenomegaly
Frontal bossing
“Hair on end” appearance to skull
Spinal cord compression

33
Q

What is the management of beta thal major?

A

Regular transfusion programme to maintain Hb at 95-105 g/L (suppresses ineffective erythropoiesis and inhibits over-absorption of iron)

34
Q

What does regular blood transfusions allow for in beta thal major?

A

Normal growth and development
Iron overload from transfusion then becomes the main cause of mortality
Bone marrow transplant may be an option if carried out before complications develop

35
Q

What are the consequences for iron overload?

A

Endocrine; impaired growth and pubertal development
Diabetes
Osteoporosis
Cardiac: cardiomyopathy, arrhythmias
Liver disease: cirrhosis, hepatocellular cancer

36
Q

Why is iron overload so common in beta thal major/

A

Each unit of red cells contains 250mg
In beta thal major you will give 2-3 units every 3 weeks
Chronic anaemia drives increased iron absorption
Venesection not feasible as already anaemic

37
Q

What is the treatment for iron overload in beta thal major?

A

Iron chelating drugs e.g. desferrioxamine

Chelators will bind to iron which is then excreted

38
Q

What are complications specific to blood transfusions in beta thal major?

A

Viral infection; HIV, hep B and C
Alloantibodies
Transfusion reactions
Increased risk of sepsis

39
Q

What causes sickle cell disease?

A

Point mutation in codon 6 of the beta globulin gene that substitutes glutamine to valine producing betaS

40
Q

Why will cells with beta S sickle?

A

HbS polymerizes if exposed to low oxygen levels for a prolonged period of time
This will distort the cell, damaging the RBC membrane

41
Q

What is the genotype of sickle cell trait?

A 
HbAS 
One normal, one abnormal beta gene 
Asymptomatic carrier state 
May sickle in severe hypoxia
Blood film NORMAL
42
Q

What will be seen on the blood film in HbSS?

A

Sickle cells

Target cells

43
Q

What are the consequences of sickle cell anaemia?

A 
Sickle crisis 
Chronic haemolysis 
Sequestration of sickled RBCs in liver and spleen 
Prothrombotic 
Hyposplenism (repeated splenic infarcts)
44
Q

What causes a sickle crisis?

A

Sickle vaso-occulsion

Results in tissue ischaemia and pain

45
Q

What can precipitate a sickle crisis?

A 
Hypoxia
Dehydration 
Infection 
Cold exposure 
Stress/ fatigue
46
Q

How is a sickle crisis treated?

A 
Opiate analgesia 
Hydration 
Rest 
Oxygen 
Antibiotics if evidence of infection 
Red cell exchange transfusion
47
Q

When is a red cell exchange transfusion indicated?

A

Severe crisis;
Lung (vicious cycle of chronic hypoxia)
Brain (stroke)

48
Q

What is the long term management of sickle cell anaemia?

A 
Hyposplenism infection risk: 
HiB, meningococcus and pneumococcus vaccination. 
Penicillin prophylaxis 
Folic acid supplementation 
Vit B12 (induce HbF production) 
Regular transfusion
49
Q

How is infection risk reduced in hyposplenism?

A

Prophylactic penicillin

Vaccination; pneumococcus, meningococcus, haemophilus

50
Q

What bacteria are those with hyposplenism most susceptible to?

A

Encapsulated organisms - pneumococcus, meningococcus, haemophilus

51
Q

What is HPLC used for?

A

Quantify Hb present; identified HbS, HbH and a raised HbA2

Haematology (31 decks)

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