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HAEMATOLOGY > Haemoglobinopathies > Flashcards

Haemoglobinopathies Flashcards

1
Q

How many Haem groups are there per globin chain?

A

1 per globin chain => 4 per Hb molecule (each can pick up one O2)

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2
Q

What are the major forms of Hb?

A

HbA (α2β2 ), HbA2 (α2δ2) HbF (α2γ2)

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3
Q

What chromosomes control globin chain production?

A

Alpha genes (aa,aa) chromosome 16, Beta genes (bb) chromosome 11

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4
Q

When does adult haemoglobin (HbA) production take over from foetal haemoglobin (HbF)?

A

6-12 months of age

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5
Q

How are haemoglobinopathies genetically inherited?

A

autosomal recessive

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6
Q

What are the two main groups of haemoglobinopathies?

A

Thalassaemias (less globin chain synthesis), Structural haemoglobin variants (normal production but chain abnormal)

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7
Q

What globin chains can be affected in a thalassemia?

A

Alpha thalassaemia (α chains), Beta thalassaemia (β chains)

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8
Q

What are the possible consequences of a thalassemia?

A

Accumulation of globin chains (toxic to cell), Haemolysis, Ineffective erythropoiesis

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9
Q

Where in the world are thalassemias most prevalent?

A

Africa and Asia

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10
Q

What are the different types of alpha thalassemia (based on the number of working genes)?

A

Unaffected = 4 normal α genes (αα/αα)

TRAIT = one or two alpha genes missing

HbH = only one alpha gene left (–/-α )

Hb Barts hydrops fetalis = NO functional α genes (–/–)

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11
Q

Patients with alpha thalassemia trait will be asymptomatic. TRUE/FALSE?

A

TRUE

- no treatment req’d

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12
Q

HOw do RBCs appear on a blood film of a patient with an alpha thalassemia trait? What is this similar to, and how are the two distinguished?

A

Microcytic, hypochromic red cells with mild anaemia

Similar to iron deficiency
=> but FERRITIN NORMAL

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13
Q

Describe the blood results of a patient with HbH disease?

A

Anaemia with very low MCV and MCH

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14
Q

How is HbH formed in HbH disease?

A

Excess β chains form tetramers (β4)

as no alpha chains to bind to

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15
Q

Where is HbH disease (and alpha thalassemias in general) most common?

A

South East Asia

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16
Q

HOw may patients with HbH disease present, and what treatment may they require?

A

Jaundice and splenomegaly

Patients may need transfusion

17
Q

What is Hb Barts Hydrops Foetalis?

A
  • Severest form of α thalassaemia
  • Minimal or no α chain production
    => HbF and HbA can’t be made
  • Instead tetramers of Hb Barts (γ4) and HbH (β4) produced
18
Q

Where in the world is there a higher risk of Hb Barts Hydrops Foetalis?

A

Risk if both parents from SE Asia

- as this is where α0 (–) thalassemia trait prevalent

19
Q

How is the risk of Hb Barts Hydrops Foetalis minimised?

A

Antenatal screening

20
Q

Babies who are born with Hydrops Foetalis have what distinct clinical features?

A
  • Profound anaemia
  • Cardiac failure
  • Growth retardation
  • Severe hepatosplenomegaly
  • Skeletal and cardiovascular abnormalities
    • HOWEVER Almost all die in utero**
21
Q

What type of Hb production is affected in beta thalassemias?

A

HbA (α2β2) affected

=> as only β chains depleted

22
Q

What are the different classifications of beta thalassemia?

A

β thalassaemia trait

  • Asymptomatic
  • No/mild anaemia
  • Low MCV/MCH
  • Raised HbA2 diagnostic

β thalassaemia intermedia

  • Moderate severity
  • requires occasional transfusion

β thalassaemia major (β0/β0)

  • Severe
  • Lifelong transfusions
23
Q

When does Beta thalassemia major usually present?

A

Presents aged 6-24 months (as HbF falls)

24
Q

What Hb is found in beta thalassemia major?

A

Mainly HbF

No HbA

25
Q

HOw do patients with beta thalassemia major usually present clinically.

A
  • Pallor, failure to thrive
  • Skeletal changes (erythropoiesis in skull e.g frontal bossing)
  • Hepatosplenomegaly
  • Organ damage
26
Q

What is a potential consequence of extramedullary haematopoiesis in the vertebrae?

A

Spinal cord compression

27
Q

What are the main causes of death in beta thalassemia major once patients are ON treatment?

A
  • Iron overload from transfusions
  • deposits in organs causing damage/failure
    e. g. pituitary (inhibits growth/puberty), causes cardiac arrythmias, liver cirrhosis/ HCC
28
Q

HOw can beta thalassemia be cured?

A

Bone marrow transplant (if carried out before complications develop)

29
Q

How is iron overload due to transfusion treated?

A

cant venesect - this revereses transfusion!

=> Iron chelating drugs (eg desferrioxamine)
=> bind to iron which is then excreted

30
Q

Describe the pathophysiology of sickle cell anaemia

A
  • Point mutation in β globin gene
  • alters structure of Hb→ HbS
  • HbS polymerises if exposed to low O2 for long time
  • distorts red cell => damaging RBC membrane
31
Q

What is sickle cell trait and are patients usually symptomatic?

A
  • One normal and one abnormal β gene
  • Asymptomatic as HbS level too low to polymerise
  • May sickle in severe hypoxia (eg high altitude or anaesthesia)
32
Q

What is the main type of Hb found in patients with sickle cell trait?

A

Mainly HbA, HbS <50%

33
Q

What happens to Hb sickle cell disease (HbSS)?

A
  • Two abnormal β genes (βs/βs)

- Patients have mainly HbS (> 80%) and no HbA

34
Q

What symptoms are experienced by patients with sickle cell anaemia?

A
  • Episodes of tissue infarction due to vascular occlusion by odd shaped sickle cells
    => sickle crisis
  • Pain may be extremely severe
  • Hyposplenism due to repeated splenic infarcts
  • Chronic haemolysis – shortened RBC lifespan
  • Sequestration of sickled RBCs in liver and spleen
35
Q

What can precipitate a sickle cell crisis?

A 
Hypoxia ‏
Dehydration
Infection
Cold exposure
Stress/fatigue
36
Q

HOw is a sickle cell crisis treated?

A
  • Opiates
  • Hydration
  • Rest
  • Oxygen
  • Antibiotics if evidence of infection
  • Red cell exchange transfusion (venesect/tranfuse and repeat)
    => in severe crisis eg (lung) chest crisis or (brain)stroke
37
Q

How is sickle cell anaemia managed in the long term?

A
  • prophylactic penicillin for hyposplenism
  • vaccinations for hyposplenism => pneumococcus, meningococcus, haemophilus
  • Folic acid supplementation (↑ RBC turnover so ↑demand)
  • Regular transfusion to prevent stroke
38
Q

How should you approach a potential haemoglobinopathy?

A
  • FBC - Hb, red cell indices
  • Blood film
  • Ethnic origin
  • Liquid chromatography OR electrophoresis to quantify Hb present
  • Identify abnormal haemoglobins
  • Raised HbA2 diagnostic of beta thal trait

HAEMATOLOGY (24 decks)

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