Week 1: Genetics of blood

Question 1

How many systems are there for classifying blood types?

Answer 1

30

Question 2

What are blood group systems based on?

Answer 2

cell surface and or soluble antigens

Question 3

What are the role of blood group antigens?

Answer 3

Question 4

What are the A and B antigens

Answer 4

They are carbohydrate structures present on red blood cell membrane glycoprotein and glycolipids.

Question 5

What are the major carriers of A and B antigens on red cells?

Answer 5

The abundant N-glycosylated glycoproteins, the anion exchanger (band 3) and the glucose transporter (GLUT1)

Question 6

The gene that encodes type A antigens encode for what?

Answer 6

N-acetylgalactosaminyltransferase

Question 7

The gene that encodes type B encodes for what?

Answer 7

Galactosyltransferase

Question 8

The gene that encodes for type O (H) encodes for what transferase?

Answer 8

No transferase

Question 9

What chromosome is ABO gene encoded on?

Answer 9

chromosome 9

Question 10

What is another name for antigen in terms of i, IA and IB?

Answer 10

Isoagglutinogen because the RBCs will agglutinate upon exposure to its antibody

Question 11

Why can you not give blood group A to someone who is blood group B?

Answer 11

They will have anti A antibodies which can cause a transfusion reaction.

Question 12

What are the 5 major Rh antigens?

Answer 12

D, C, c, E, e

most immunogenic is D

Question 13

What is the genotype to express the D antigen?

Answer 13

They need 1 or both alleles

Question 14

Are there any anti D antibodies present in blood?

Answer 14

No

Question 15

What is rhesus disease?

Answer 15

a condition where antibodies in a pregnant woman’s blood destroy her baby’s blood cells. Rhesus disease doesn’t harm the mother, but it can cause the baby to become anaemic and develop jaundice. usually when the mother is rh negative and father is rh positive.

Question 16

What is sensitisation?

Answer 16

When the mother is exposed to the RhD positve antigens which means that the mother will start making antibodies against the foreign red blood cells

Question 17

What is the range in effect of Rhesus disease of newborn babies?

Answer 17

Ranges from mild anaemia to intrauterine death at 18 weeks of gestation fails - hydrops fetalis

Question 18

What is kernicterus?

Answer 18

A complication of severe jaundice which leads to brain damage in severe cases of mild deafness.

Question 19

What is antenatal serology?

Answer 19

Prenatal testing by blood group determination and identification of atypical antibodies associated with haemolytic disease of the newborn and microbiology screening.

Question 20

What is Anti - D therapy?

Answer 20

The anti-D immunoglobulin neutralises any RhD positive antigens that may have entered the mother’s blood during pregnancy. If the antigens have been neutralised, the mother’s blood won’t produce antibodies.

Question 21

What is the universal blood group recipient?

Answer 21

AB+

Question 22

What is the universal blood group donor?

Answer 22

O-

Question 23

What is SC anaemia caused by?

Answer 23

Caused by a change in the quality of the ß globin chain

Question 24

What is Thalassaemia?

Answer 24

Caused by a reduction in the quantity of the alpha or beta-globin chain.

Question 25

Where is the mututation in sickle cell?

Answer 25

Mutation of HBB gene on chromosome 11 - glutamic acid replaced by valine - gene form termed HBS
Alters Hb affinity for O2
Under deoxygenated conditions Hb tetramers with a mutated β-globin chain have the tendency to complex forming polymers which cause distortion of the RBC.
Individuals with only one copy of mutated β-globin gene are able to complex but less efficiently

Question 26

What does the incidence of malaria correlate with ?

Answer 26

The endemicity of Plasmodium falciparum

Question 27

What is the clinical presentation of sc anaemia?

Answer 27

Episodes of severe haemolytic anaemia
Vaso-occlusive episodes - crises with possible infarcts in bones, lung, spleen, brain
More susceptible to infections
Sickle cell trait may present with minor symptoms

Impact on daily life.

Question 28

How many people have SC anaemia and thalasaemia?

Answer 28

13000-15000 and 1000 respectively

Question 29

Clincial Management for SC?

Answer 29

Prophylaxis: reduce risk of infection e.g Pneumococcal vaccination, Folic acid supplements, Prophylactic penicillin, Spleen size determination, Lifestyle modification
Bone marrow or stem cell transplant may be curative but risky treatment. Not a common approach.
Management: may include blood transfusions at intervals.
Prevention: genetic screening – antenatal screening of parents and postnatal screening of baby
NHS – sickle cell screening programme
Education: genetic counselling and support to manage disease – Sickle Cell Centres.