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Year 1 > Genetics of blood > Flashcards

Genetics of blood Flashcards

1
Q

What is blood type?

A

Classification of blood based on cell surface proteins such as antigens and the rhesus factor.

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2
Q

What is the role of antigens and antibodies in blood typing?

A

Determining an individuals blood group. There are 4 blood groups, A, B, O and ABO. It corresponds to whether they have the A antigen, B antigen, both A and B antigen or neither.

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3
Q

What are the blood antigens?

A

A and B antigens are carbohydrate structures which attach to glycolipids or glycoproteins on erythrocyte membranes which form interactions that determine blood type via glycosyltransferase enzyme catalysation.

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4
Q

What are glycosyltransfersases?

A

Enzymes which determine blood type via catalysing the transfer of antigen carbohydrate structures to proteins on the erythrocyte membrane such as anion exchanger, GLUT1 and N-glycosylated glycoproteins. A antigen means group A, etc…

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5
Q

How are glycosyltransferases synthesised?

A

It is an enzyme encoded by genes in the nucleus. There are only 2 forms because there are only 2 antigens. Galactosyltransferase and N-acetylgalactosaminyltransferase.

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6
Q

What are the carriers of A and B antigens on erythrocytes?

A

Glycoproteins, band 3 anion exchangers and GLUT 1 glucose transporter

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7
Q

What is the role of Band 3 anion exchangers in the blood?

A

Carrier for A or B antigens which is catalysed by glycosyltransferase enzyme. It is also responsible for the chloride shift between HCO3- and CL- for the delivery of O2 to metabolically active tissues.

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8
Q

What is the role of GLUT transporters in the blood?

A

They uptake glucose in response to insulin levels. They are carriers for the A or B antigens which is catalysed by glucosyltransferase enzyme.

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9
Q

What is the gene encoding for glycosyltransferase in Type A individuals?

A

N-acetylgalactosaminyltransferase

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10
Q

What is the gene encoding for glycosyltransferase in Type B individuals?

A

Galactosyltransferase

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11
Q

What is the gene encoding for glycosyltransferase in Type O individuals?

A

No transferase because no antigen is present

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12
Q

What is the mechanism of action of glycosyltransferases?

A

The acceptor substrate for the antigen transferases is the H antigen. N-acetylaminogalactotransferase catalyses the transfer of the A antigen N-acetylgalactosamine from UDP N-acetylgalactosamine to the H antigen. Galactosyltransferase catalyses the transfer of the B antigen galactosyl from UDP-galactosyl to H antigen.

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13
Q

How are blood groups inherited?

A

Non-Mendelian inheritance encoded by one gene on Chromosome 9. This has 3 allelic variants.

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14
Q

What are isoagglutinogens?

A

Antibodies produced against foreign blood group antigens that causes agglutination of the RBC with the foreign antigen. A person with Type B group will produce antibodies against A.

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15
Q

Which isoagglutinogens will be produced for a Type A individual?

A

Anti-B antibodies.

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16
Q

Which isoagglutinogens will be produced for a Type B individual?

A

Anti-A antibodies

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17
Q

Which isoagglutinogens will be produced for a Type O individual?

A

Anti-A and Anti-B

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18
Q

Which isoagglutinogens will be produced for a Type O individual?

A

Both Anti-A antibodies and Anti-B.

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19
Q

What is Rh?

A

Also known as Rhesus factor, it is a cell surface protein on blood cells which give blood types a positive or negative depending on if it is present. It is an importnant indicator of compatibility.

20
Q

What are the types of Rh?

A

5 antigens classifications of Rh:
RHC
RHc
RHD
RHE
RHe.
The most immunogenic is RhD.

21
Q

How is the Rh antigen produced?

A

Encoded by both RHD and RHCE genes

22
Q

How is Rhesus factor produced?

A

Rhesus factor is encoded by RHD gene which encodes for RHD and RHCE gene which encodes for RHC/c and RHE/e.

23
Q

How is RhD inherited?

A

Individuals who are RHD+ may be homozygous or hemizygous for RHD gene. As long as they have one copy of the RHD gene, they will express RHD on all erythrocytes.

24
Q

Why are some individuals RHD-?

A

The RHD gene has been deleted so there is no expression of the D antigen.

25
Q

What is Rhesus disease?

A

When a RH- mother carries a RH+ foetus. Antigens from foetus can enter the mother’s blood during delivery and cause sensitisation which promotes the production of anti-RH antibodies. In response to this, subsequent pregnancy with a RH+ foetus will result in anti-RH maternal antibodies crossing placenta to damage the foetal RBC.

26
Q

What are the implications of Rhesus disease?

A

Can cause anaemia and jaundice which may develop into Kernicterus and lead to intrauterine death

27
Q

How is Rhesus disease treated?

A

Prophylaxis with Anti-RHD therapy that neutralises any RHD+ cells to prevent production of maternal antibodies.

28
Q

What is hydrops fetalis?

A

Foetus or baby with anaemia has severe fluid build up due to too much blood leaving bloodstream and entering tissues.

29
Q

What is Kernicterus?

A

Brain damage in babies caused by bilirubin build up as a result of untreated jaundice caused by haemolytic anaemia. A complication of Rhesus disease.

30
Q

Which group is a universal recipient?

A

Group AB+ which makes up 2% of donors.

31
Q

Which group is the universal donor?

A

Group O- which makes up only 12% of total donors.

32
Q

What is agglutination?

A

Immune response facillitated by antigen-antobody interactions that causes clumping. Agglutination indicates blood type for A and B antigens and RH factor.

33
Q

What is thalassaemia?

A

A type of haemoglobinopathy caused by reduction in quantity of alpha or beta globin chain.

34
Q

What is the cause of sickle cell anaemia?

A

Missense mutation of HBB gene replaces glutamic amino acid with valine amino acid and creates a HBS gene.

35
Q

How does sickle cell anaemia affect HB in hypoxic conditions?

A

It will complex and polymerise due to valine amino acid and this will distort the shape of RBC, disrupting its ability to travel through capillaries. Results in vaso-occlusion that causes episodic pain.

36
Q

Difference between sickle cell and thalassemia?

A

Thalassemia is when not enough globin chains are produced. Sickle cell is when the synthesis of the globin chains results in distorted shape.

37
Q

What is the world incidence of thalassemia?

A

Meditteranean, South and Southeast asian and Middleastern origin

38
Q

What is the world incidence of sickle cell anaemia?

A

African or carribean descent. Correlates with prevalence of plasmodium falciparum (mosquito) which has a selective survival advantage for individuals with AS genotype against malaria. Those with sickle cell anaemia have a worse outcome for malaria

39
Q

How are people with sickle cell trait impacted?

A

Mutated beta globin chain complexes less efficiently and have less symptoms. Genotype AS.

40
Q

What are the symptoms for sickle cell anaemia?

A

Vaso-occlusive episodes of pain in the bones, lung, spleen and brain. Severe haemolytic anaemia episodes. It may impact their daily life and reduces their lifespan.

41
Q

What is a venesection?

A

Drawing blood.

42
Q

How is polycythaemia treated?

A

Venesections, taking hydroxycarbamide medication and interferon.

43
Q

What are the symptoms of polycythaemia?

A

Flushed skin, itching, bleeding, tingling in hands or feet, feeling of fullness and swollen spleen.

44
Q

What is hydroxycarbamide?

A

A chemotherapy drug which inhibits DNA synthesis for RBC production to treat polycythaemia. Increases risk of infection and GI discomfort.

45
Q

Interferon alpha

A

Drug derived from the human cytokine interferon for immune defence, used to treat side effect of hydroxycarbamide.

46
Q

Megaloblastic anaemia

A

Large nucleated RBCs caused by B12 or folate deficiency

47
Q

Consequences of macrocytic anaemia

A

Damage to the nervous system and neurological complications due to low O2 levels

Year 1 (191 decks)

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