haemoglobin and thalassemia

Question 1

when synthesis of haemoglobin occurs and why

Answer 1

during development of RBC, mostly in erythroblast stage, but also reticulocyte stage because RBC have no nucleus or MITOCHONDRIA, so synthesis must occur during RBC development

Question 2

structure of haemoglobin and where haem and globin produced

Answer 2

2 alpha and 2 beta chains for HbA haem produced in mitochondria- Fe2+ endocytoses into cell as transferrin, and released: synthesis regulated by enzyme ALAS: when too much produce, - feedback occurs globin chains produced in ribosomes in cytosol

Question 3

haem component- what its made out and what molecules have it

Answer 3

combination of protoporphyrin ring with central Fe atom= Fe combines with oxygen also present in other proteins like myoglobin and peroxidases

Question 4

globin synthesis- clusters, chains formed and defects DIAGRAM

Answer 4

8 types of globin chains formed by 2 clusters- beta (Chr 11) and alpha (Chr 16) cluster alpha cluster forms embryonic globin chain called azita chain, and alpha chains- azita chains die off after 6 weeks, so embryo reliant on alpha chains- defect of alpha cluster= alpha thalassemia= affects early at embryonic stage beta chains important for foetal and adult globin chains, including delta, gamma- form gamma chains for foetus, then beta chain after birth- defect in beta cluster= beta thalassemia= presents 5 months after birth (as foetus/baby can survive few months with alpha and gamma chains ie foetal haemoglobin)

Question 5

adult haemoglobins + electrophoresis DIAGRAM

Answer 5

HbA (97%), Hb A2 (alpha and delta-2%) and HbF (alpha and gamma- 1%) in electrophoresis , HbF left of HbA, HbA2 right to HbA

Question 6

globin structure- secondary and tertiary

Answer 6

secondary structure has helical arrangment, and tertiary forms a sphere, with hydrophilic surface, and hydrophobic core, with a haem pocket (wher O2 can access)

Question 7

oxy vs deoxyhaemoglobin

Answer 7

higher conc of 2,3 DPG in deoxyhaemoglobin changes shape of globin chains, preventing O2 accessing the haem POCKET

Question 8

p50 and use

Answer 8

partial pressure of O2 where 50% Hb bound to O2- used to compare affinities of different haemoglobins

Question 9

factors affecting dissociation curve

Answer 9

HbF, decrease ins 2,3 DPG and increased pH/low CO2a shifts curve to left (higher affinity), opposite and HbS shifts curve to right

Question 10

2 types of haemoglobinopathies and important point

Answer 10

either due to mutation causing structural change in haemoglobin, or less globin chain synthesiss ie thalassemia HAEM ALWAYS SAME, DEFECTS ONLY DUE TO GLOBIN PART

Question 11

classification of thalassemia

Answer 11

either by globin type affect (alpha/beta), or by severity (minor/trait= asymptomatic as carrier, intermedia possibly symptomatic, major NEEDS transfusions as both genes mutated)

Question 12

beta thalassemia- cause, how many genes and prevalence

Answer 12

mutation of beta globin gene= fewer beta globin chains there are 2 beta genes- if heterozygous, you are carrier prevalent in mediterranean coutnries, africa and south asia

Question 13

inheritance of beta thalassemia

Answer 13

autosomal recessive- if two carriers mate, there is 25% chance of child being a major carriers can either be BB0 or BB+- B+ means it’s partially defective, B0 means no chains can be produced, so child with B0B+ is intermediate, as one gene not COMPLETELY defective

Question 14

diagnosis of thalassema

Answer 14

full blood count- low MCV, Hb only slgihtly reduced

film- target cell and poikilocytosis (vary in shape eg teardrop): should be hypochromic (greater central pallor due to less haemoglobin) and microcytic (smaller in size), as thalaseemia microcytic

can also see nucleated red blood cells HPLC (electrophoresis)- beta shows raised HbA2 and HbF (normal HbA due to normal alpha chain), alpha difficult as normal HbA2/HbF globin chain analysis- often for alpha thalassemia

Question 15

featurs of thalasseamia major

Answer 15

hepatosplenomegaly- liver and spleen sense low haemoglobin so enlarge to do more haematopoesis bone marrow do erythroid hyperplasia blood film

Question 16

clinical features of beta thalassemia and effect of excess iron

Answer 16

fatigue, jaundice (alpha chains without beta more vulnerable to haemolysis), delay in growth/puberty, hepatosplenomegaly, skeletal issues and excess iron excess iron can lead to cardiac and liver failure, as well as endocrine issues with pituitary

Question 17

causes of death in beta thalassemai

Answer 17

mainly due to cardiac failure from iron overload- also infections and liver disease

Question 18

treatment of thalassemia major

Answer 18

1st line treatment is regular transfusions and iron chelation (transfusions exacerbate iron overload, so need to reduce it) splenectomy may be needed if transfusion requirement very high, hormone therapy for endocrine issues, hydroxyurea to boost HbF, and bone marrow transplants (only curative treatment)

if thinking of having child, look at partner, and genetic counselling if needed

Question 19

how transfusions given

Answer 19

must match red cells of donor to patient to prevent immune attack give every 2-4 weeks

Question 20

managing infection

Answer 20

often infected by organisms that like iron eg yersinia, so prophylaxis ie antibiotics needed

Question 21

when and how iron chelation therapy given and example

Answer 21

after 10-12 transfusions, eg DFO given via injection newer forms given orally, takes less time to give (3-4 hrs vs 12 hrs)- can also be used in combination

Question 22

importance of iron chelation, compliance and hwo i

Answer 22

has dramatically increased survival due to complications of iron overload those with lower compliance ( ie don’t want to do it as takes very long )to DFO survive less

Question 23

side effects of iron chelation

Answer 23

newer forms cause GI symptoms and liver/renal issues DFO can cause skeletal issues, renal issues, and increased infection risk (due to drop in WBC)

Question 24

monitoring iron overload

Answer 24

serum ferritin (protein that stores iron) liver biopsy (rarely done) hepatic/cardiac MRI- newer form of MRI called R2 MRI looks at liver iron conc

Question 25

HbH disease and alpha thalassemia

Answer 25

there are 4 alpha globin genes- problems with 3 of them causes HbH disease (intermedia), where shapes are varied, but central pallor not so big as

Question 26

HPLC for HbH disease

Answer 26

should see random peaks left of HbA peak eg HbH

Question 27

test what kind of jaundice

Answer 27

conjugated and unconjugated levels

Question 28

haemolytic uraemic syndrome

Answer 28

most common cause of renal failure in children- dark urine, haemolytic (prehaptic) jaundice, high reticulocyte count (due to haemolysis), red cell fragments in blood film