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HAEMATOLOGY > Haemoglobinopathy > Flashcards

Haemoglobinopathy Flashcards

1
Q

Describe the structure of haemoglobin

A

2 alpha and 2 beta chains

One haem group attached to each

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2
Q

What are the 3 major forms of Hb?

A

HbA (2 alpha and 2 beta)

HbA2 (2 alpha ad 2 delta)

HbF (fetal haemoglobin)

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3
Q

Alpha and beta genes are on which chromosomes?

A

Alpha gene is on chromosome 16

Beta gene is on chromosome 11

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4
Q

How many alpha and beta genes are there per chromosome and cell?

A

2 alpha genes per chromosome - 4 per cell

1 beta gene per chromosome - 2 per cell

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5
Q

When are adult levels of haemoglobin reached in infancy?

A

At 6-12 months

Before this HbF predominates

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6
Q

Are hereditary conditions affecting globing chain synthesis usually autosomal recessive or autosomal dominant?

A

Usually autosomal recessive

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7
Q

What are the 2 main groups of haemoglobinopathy?

A

Thalassaemias
(Decreased rate of globin chain synthesis)

Structural haemoglobin variants
(normal production of structurally abnormal globin chains)

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8
Q

What investigations can be done for haemoglobinopathies?

A

Genetic screening

FBCs and Hb

HPLC (high performance liquid chromatography)

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9
Q

What is HPLC (high performance liquid chromatography)? What would it show in alpha vs beta that trait?

A

A test for haemoglobinopathies which involves identifying and quantifying haemoglobins that are present

HPLC is normal in alpha that trait so DNA testing is required

HPLC shows raised HbA2 in beta that trait

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10
Q

Thalassaemias cause what type of anaemia?

A

Microcytic hypochromic anaemia

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11
Q

What types of Hb are affected in patients with alpha thalassaemia?

A

Alpha chains are present in all forms of Hb, therefore HbA, HbA2 and HbF are all affected

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12
Q

What is the genetic problem in alpha that trait?

A

There are 1-2 alpha genes missing

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13
Q

What is the genetic problem in HbH disease?

A

There is only 1 functional alpha gene

There are not enough alpha chains, so excess B chains form tetramers called HbH which can’t carry oxygen

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14
Q

People from which parts of the world are most likely to be affected by HbH disease?

A

SE Asia

Middle East

Mediterranean

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15
Q

Why does splenomegaly occur in HbH disease?

A

Due to extra medullar haematopoiesis

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16
Q

Why does jaundice occur in HbH disease?

A

Haemolysis and ineffective erythropoiesis

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17
Q

How is HbH disease managed?

A

There is a big clinical spectrum varying from moderate anaemia to transfusion dependent conditions

Severe cases will need splenectomy +/- transfusions

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18
Q

What is Hb barts hydrops fetalis syndrome?

A

Most severe form of a thalassaemia in which no a genes are inherited from either parents and there is therefore minimal or no a chain production.

HbA and HbF can’t be made and thus Hb Barts and HbH form the majority of Hb at birth.

19
Q

How does Hb barts hydrops fettles syndrome present clinically?

A

Sevre anaemia

Serve hepatosplenomegaly

Cardiac failure

Growth retardation and skeletal abnormalities

ALMOST ALL DIE IN UTERO

20
Q

What is alpha thalassaemia?

A

Disorder of alpha chain synthesis

21
Q

What is beta thalassamia?

A

Disorder of beta chain synthesis

22
Q

What kind of mutations most commonly cause beta thalassaemia?

A

Point mutations

23
Q

Which form(s) of Hb are affected in beta thalassaemia?

A

Only HbA is affected

24
Q

How does B thalassaemia trait present?

A

Asymptomatic or mild anaemia

Low MCV, raised HbA2

25
Q

How does B thalassamia intermedia present?

A

Simiar clinical picture to HbH disease

Moderate severity anaemia requiring ocasional transfusions

26
Q

When does B thalassaemia major present?

A

Presents at 6-24 months as HbF falls

27
Q

What would haemoglobin analysis show in B thalassamia major?

A

Mainly HbF and minimal HbA

28
Q

How does B thalassaemia major present?

A

Failure to thrive

Pallor

Hepatosplenomegaly

Skeletal changes

Organ damage

Risk of cord compression

29
Q

Regular transfusion can be performed to manage B thalassaemia major. What is the aim for the levels of Hb?

A

95-105g/L

30
Q

What are the treatment options for B thalassaemia major?

A

Regular transfusion

Bone marrow transplant (if carried out before complications develop)

31
Q

Iron overload can occur as a consequence of regular transfusion in patients with beta thalassaemia major. How does this present?

A

Similar clinical picture to haemochromatosis but much more severe and early onset

Endocrine dysfunction and diabetes

Impaired growth and pubertal development

Osteoporosis

Cardiac disease

Liver disease

32
Q

How can ion overload be managed?( e.g due to regular transfusions in patients with b thal major)

A

NB venesection is not an option if the patient is already anaemic (chronic anaemia drives increased iron absorption so this is why they have been overloaded, but venesection would still worsen the underlying problem)

Iron chelating drugs e.g desferrioxamine
*the chelators bind to iron to form complexes which are excreted in urine or stool

33
Q

Are sickling disorders autosomal recessive or autosomal dominant?

A

Autosomal recessive

34
Q

What is the pathophysiology behind sickling disorders?

A

Point mutation in B globin gene substitutes glutamine to valine, producing Bs

This alters the structure of Hb, causing HbS

HbS polymerises if it exposed to low oxygen levels for a prolonged period - this distorts the red cell, damaging the membrane

35
Q

What are the genetics behind sickle trait?

A

One normal and one abnormal B gene (B/Bs)

Mainly HbA present, HbS is <50%

36
Q

How does sickle trait present?

A

Mostly asymptomatic

May sickle in severe hypoxia (e.g high altitude and when under anaesthesia)

Blood film is normal

37
Q

What are the genetics behind sickle cell anaemia?

A

Two abnormal B genes (Bs/Bs)

There is no HbA, HbS is >80%

38
Q

How does sickle cell anaemia present?

A

SICKLE CRISIS

  • Episodes of tissue infarction due to vascular occlusion
  • Presents with extreme pain
  • May result in impaired growth and end-organ damage
  • Symptoms depend on the site affected
39
Q

What site is most likely to be affected in children presenting with sickle crisis?

A

Digits - causes dactylitis

40
Q

How is sickle crisis managed?

A

Opiates

Oxygen

Antibiotics (if infection is present)

Red cell exchange transfusion (involves venesection and then transfusion of donor blood)

Hydration and rest

41
Q

Does sickle cell anaemia result in splenomegaly or hyposplenism?

A

Hyposplenism

This is due to repeated splenic infarcts

42
Q

What is sickle cell disease?

A

Compound heterozygosity for HbS and another B chain mutation

E.g HbS/ B thalassaemia

43
Q

How are sickling disorders managed long-term?

not the management of sickle cell crisis

A

Folic acid supplements
(there is increased RBC turnover so increased demand)

Hydroxycarbamide (can reduce severity of the disease by inducing HbF production)

Regular transfusion

Management of hyposplenism

44
Q

How is hyposplenism in sickle cell disease managed?

A

Prophylactic penicillin lifelong

Vaccinations; pneumococcus, meningococcus and haemophilus

HAEMATOLOGY (10 decks)

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