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MET3B > Haemoglobinopathies > Flashcards

Haemoglobinopathies Flashcards

1
Q

What are the globin subunits for alpha hemoglobin?

A

Two alpha globin subunits and two beta subunits

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2
Q

How many genes code for alpha hemoglobin? On which chromosome are these genes located on?

A

There are two genes for the alpha subunit on chromosome 16

so each person has 4 genes for alpha subunit of alpha heamoglobin

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3
Q

How many genes are there for beta subunits? On which chromosome are they located on?

A

5 genes

Chromosome 11

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4
Q

What are the names of the 5 genes which code for the beta subunits?

A

epsilon, gamma A, gamma G, delta and beta

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5
Q

Another gene for another globin subunit is also located on ch 16. What is it called?

A

Zeta subunit

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6
Q

What are the globin subunits for HbF hemoglobin?

A

alpha x2

Gamma x2

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7
Q

What are the globin subunits for HBA2 hemoglobin?

A

alpha x2

Delta x2

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8
Q

What are the globin subunits for Hb grower 1 embryo hemoglobin?

A

Zeta x 2

Epsilon x 2

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9
Q

What is the name of the first form of haemoglobin produced in the yolk sac? How long does it last?

A

Hb Gower-1

6 weeks

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10
Q

Where in the body is Fetal Haemoglobin (HbF) produced?

A

liver and spleen

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11
Q

What is the main different between fetal hemoglobin and maternal hemoglobin?

A

Fetal hemoglobin has a higher affinity for oxygen than maternal Hb
So O2 is transferred from maternal blood to foetal blood

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12
Q

When does fetal hemoglobin change into HbA?

A

3-6 months after birth

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13
Q

What are the 2 main variations of grower hemoglobin?

A

Gower 2 a2 epsilon2 and Portland zeta2 Epsilon2.

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14
Q

How does alpha thalassaemia often develop?

A

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

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15
Q

How does beta thalassaemia often develop?

A

when there is a point mutation on chromosome 11

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16
Q

What is the name of the condition caused by One alpha hemoglobin gene defective? How does it present?

A

Alpha thalassemia minima

  • No clinical symptoms

May have a slightly reduced mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH).

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17
Q

What is the name of the condition caused by two alpha hemoglobin gene defective? How does it present?

A

alpha thalassemia minor

  • Mild microcytic hypochromic anemia
  • Can be mistaken for iron deficiency anemia and treated inappropriately with iron.
18
Q

What is the name of the condition caused by three alpha hemoglobin gene defective? How does it present?

A

Haemoglobin H disease

Two unstable haemoglobins are present in the blood: Haemoglobin Barts (γ4) and Haemoglobin H (β4).

Both have a higher than normal affinity for oxygen resulting in poor release of oxygen in tissues

moderate to severe microcytic hypochromic anemia

19
Q

What is the name of the condition caused by four alpha hemoglobin gene defective? How does it present?

A

Hydrops fetalis

Fetus cannot live independently outside the uterus and may not survive gestation

most such infants are stillborn with hydrops fetalis

have little circulating haemoglobin, and the haemoglobin that is present is all tetrameric γ chains (Haemoglobin Barts).

20
Q

What is the inheritance pattern of beta thalassemia?

A

autosomal recessive

21
Q

What are the 3 types of beta thalassemia someone can get?

A

Beta thalassaemia minor, β+
(heterozygous)

Beta thalassaemia major, βo
(homozygous)

Beta thalassemia intermedia
(both of the beta globin genes are mutated, but are still able to make some viable beta chains)

22
Q

When does beta thalassemia tend to manifest?

A

when the switch from gamma to beta chain synthesis occurs several months after birth

23
Q

In the blood of someone with beta thalassemia major you may see increased Hb F and Hb A2, why?

A

compensatory increase in gamma and delta chain synthesis

24
Q

How does beta thalassemia lead to (severe) hypochromic microcytic anaemia

A

Loss of beta globin causes the production of excess alpha globins

These form alpha tetramers which are unstable and precipitate on the erythrocyte membrane

This causes intra-medullary destruction of developing erythroblasts, erythroid hyperplasia and ineffective erythropoiesis

25
Q

What happens when beta thalassemia major is left untreated?

A
  • Sever Hypochromic, Microcytic Anaemia
  • Bone marrow expansion, splenomegaly
  • Bone deformity (frontal bossing, hypertrophy of maxilla , extramedullary erythropoietic masses
  • Failure to thrive from about 6 months of age
  • Heart failure and death by age 3-4
26
Q

How is beta thalassemia major treated?

A

Regular transfusions
This can cause iron overload so - Iron chelation therapy

Allogeneic bone marrow transplant (for young children if sibling donor available)

27
Q

How to distinguish iron deficiency anaemia from thalassaemia?

A

In thalassaemia, although red cells are microcytic, serum iron and ferritin are normal

28
Q

What effect does iron overload have?

A

Excess iron causes
ROS as a result of the Fenton reaction are formed which in turn oxidise and damage biological tissues.

This reaction is responsible for cirrhosis, diabetes, glandular dysfunction (especially growth hormone deficiency) and other effects of chronic iron overload.

29
Q

The iron chelation therapy drug Desferoxamine, ‘Desferal is enhanced by which drug?

A

ascorbate

30
Q

Which iron chelation therapy drug can not be used during pregnancy and why?

A

Deferiprone, Ferriprox

Agranulocytosis/neutropenia may occur: Not to be used in pregnancy

31
Q

What are the side effects of the iron chelation therapy drug Deferasirox, Exjade®?

A

GI bleeding and kidney or liver failure

32
Q

Which mutation causes sickle cell disease? Which globin chain does this mutation effect?

A

point mutation – a glutamic acid to valine substitution at codon 6 of the beta globin chain.

An abnormal beta chain is produced (βS)

33
Q

How does Sickle Haemoglobin change and negatively impact the body?

A

In deoxygeneated blood haemoglobin S may precipitate or crystallize, distorting the red blood cells into a sickle shape, making them fragile and easily destroyed, leading to anaemia

Sickled red cells have decreased survival time (leading to anaemia) and tend to occlude capillaries, leading to ischemia and infarction of organs

34
Q

How so sickled cells lead to nitric oxide depletion?

A

rigid sickle cells adhere to endothelium, interact with white cells and vessel wall, cause nitric oxide depletion

35
Q

When someone has Haemolytic anaemia, what would there haemoglobin levels be in the range of?

A

6 – 8 g/dL

36
Q

What are the main clinical consequences/ symptoms of sickle cell anaemia?

A

Haemolytic anaemia

Increased susceptibility to infection

Vaso-occlusive crises

Chronic tissue damage (e.g. stroke, avascular necrosis of hip, retinopathy)

37
Q

How is sickle cell anaemia treated?

A

Infection prophylaxis and vaccination programmes
Analgesics for painful crises
Education, life style, avoidance of precipitants
Transfusions for specific acute and chronic complications
Hydroxyurea (Increases HbF, reduces painful crises)
Bone marrow transplantation

38
Q

At what age is neonatal screening for sickle cell conducted?

A

6months-2 years

39
Q

What is HAEMOGLOBIN C?

A

Mutation causing abnormal beta chain

causes reduced plasticity and flexibility of the erythrocytes

There is excess red cell destruction

40
Q

What are the clinical presentations for homozygotes and heterozygous Haemoglobin C

A

homozygotes, nearly all Hb is in the HbC form, resulting in mild haemolytic anemia.

heterozygous- only about 1/3 of total haemoglobin is in the form of HbC, and no anaemia develops.

41
Q

What is Haemoglobin E?

A

abnormal hemoglobin with a single point mutation in the β chain

Haemoglobin E disease results when the offspring inherits the gene for HbE from both parents

At birth, babies homozygous for the haemoglobin E allele do not present symptoms due to the fetal hemoglobin they still have. However after 3-6 months , fetal hemoglobin disappears and the amount of hemoglobin E increases, so the subjects start to have a mild β-thalassemia

MET3B (17 decks)

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