The Haemoglobin molecule and thallaseamia

Question 1

Summarise the key features of RBCs

Answer 1

Carry oxygen from lungs to tissues
Transfer CO2 from tissues to lungs
3.5-5 x 1012 /L (WBC ^9- so much more RBCs)
Contain haemoglobin (Hb)
Each red cell contains approximately 640 million molecules of Hb
Do not have nucleus or mitochondria

Question 2

Why is it important that Hb is packaged into RBCs

Answer 2

Hb is very toxic- strong oxidant properties

Hence in haemolytic anaemias, when RBCs lyse and release free Hb into the circulaiton- this can cause lots of damage to tissues.

Question 3

Summarise the key features of Haemoglobin

Answer 3

Found exclusively in RBCs
MW 64-64.5 kDa
Normal concentration in adults:120-165g/L
Approximately 90 mg/kg produced and destroyed in the body every day
Each gram of Hb contains 3.4mg Fe

Question 4

What is important to remember about the range of Hb concentration for females

Answer 4

Slightly less than that for males

110-165 g/L

Question 5

When does the synthesis of haemoglobin take place and why is it important that it occurs at these stages

Answer 5

Synthesis occurs during development of RBC and begins in pro-erythroblast:
65% erythroblast stage
35% reticulocyte stage

Needs to be synthesises before nucleus is lost (mature erythrocytes have no nucleus).

Question 6

Describe the basic structure of a haemoglobin molecule

Answer 6

Haemoglobin (Hb) is a protein molecule found in red blood cells. Each molecule of haemoglobin consists of 2 pairs of globin protein chains together with 4 haem groups. Each haem group consists of a protoporphyrin ring with an iron atom at its centre and a single haem group sits in a pocket formed by a single globin chain:

Haem (synthesised in mitochondria)
Globin (synthesised in ribosomes)

Question 7

Outline the synthesis of haemoglobin

Answer 7

Transferrin endocytosed in vesicle with receptor it binds to
Iron released from veiscle
Receptor and transferrin recycled in transferrin cycle
Fe can be stored as ferritin in the cell (or Fe released from ferritin)
Fe enters mitochondria
b. Glycine, B6 and Succinyl CoA create delta-ALA which then undergoes a few moderations outside the mitochondria and then passes back in as proto-porphyrin.
Proto-porphrin and Fe combine to form four haem molecules

Globin:
2.	Globin:
a.	Amino acids are used in ribosomes to create the globin chains. ( alpha and beta)
Alpha and beta chains associate (A2B2)
3.	Haemoglobin:
a.	 Globins and haem associate.

Question 8

Describe the regulation of the synthesis of haem

Answer 8

If we have too much haem
Negative feedback on delta-ALA enzyme

Hence no production of porphobilinogen
No production of uroporphrinogen
No production of Coproporphyrinogen
No production of proo-porphryin

No production of haem

Question 9

What does delta-ALA stand for

Answer 9

5-Aminolevulinic acid

Question 10

Where else is Haem found

Answer 10

Not exclusive to haemoglobin

Also contained in other proteins e.g. myoglobin, cytochromes, peroxidases, catalases, tryptophan

Question 11

Summarise the key features of haem

Answer 11

Same in all types of Hb
Combination of protoporphyrin ring with central iron atom (ferroprotoporphyrin)
Iron usually in ferrous form (Fe2+)
Able to combine reversibly with oxygen
Synthesised mainly in mitochondria which contain the enzyme ALAS
Regulation

Question 12

Summarise the key features of globin

Answer 12

Various types which combine with haem to form different haemoglobin molecules

Eight functional globin chains, arranged in two clusters:
b- cluster (b, g, d and e globin genes) on the short arm of chromosome 11
a- cluster (a and z globin genes) on the short arm of chromosome 16

Question 13

Describe the different genes in which globin chains are encoded

Answer 13

Several different types of globin proteins exist each encoded by their own gene (s). The globin genes are located in two clusters. The alpha cluster is found on chromosome 16 and contains the genes for α globin (adult variety) and ζ globin (zeta globin – an embryonic variant). The alpha genes are duplicated so that there are two functional alpha genes within an alpha cluster. (alpha 1 and 2)

The beta cluster is found on chromosome 11 and contains the genes for β globin, and δ globin (adult varieties), γ globin and ε globin (fetal and embryonic variants respectively).

Question 14

What are the embryonic variants of haemoglobin

Answer 14

Gower 1- ( 2 z and 2e)
Portland ( 2 z and 2 gamma)
Gower 2 (2 alpha and 2 e)

Question 15

What is the main fetal haemoglobin variant

Answer 15

HbF
(2 alpha and 2 gamma)

(also found in large amounts at birth)

Question 16

What are the main adult haemoglobin variants

Answer 16

HbF
HbA2- 2 alpha and 2 delta
HbA- 2 alpha and 2 beta

Question 17

What is special about the alpha globin genes

Answer 17

There are TWO alpha globin genes from each parent so there are FOUR alpha globin genes in total

Question 18

Describe globin gene expression and switching

Answer 18

§ a - is made relatively early and stays high throughout.

§ b - is equal and opposite to g and becomes dominant after birth.

§ g - is equal and opposite to b and is dominant pre-natal.

§ d - production begins mid-natal and remains low forever.

§ e and z - is equal and opposite to a and levels drop ~0 after 8 weeks.

Question 19

10. When are the genes coding for the globin in foetal haemoglobin switched off?

Answer 19

It is decreased towards birth and in the first year after birth.
After 1 year of life, the normal adult pattern of haemoglobin synthesis would have been established.

Question 20

Explain why alpha thallasaemia majors are not compatible with life

Answer 20

Due to gene expression of alpha
Expressed highly in embryonic, fetal and adult life
Therefore absence of this globin chain would mean that the fetus nor the embryo could make haemoglobin- no delivery of O2- death before birth.

Question 21

Explain why beta thalassameias are compatible with life

Answer 21

Beta globin only becomes dominant with alpha after birth (gamma before birth in embryo)
Will see symptoms 3 months after birth

Question 22

Describe the distribution of the different adult haemogloobins found in the blood

Answer 22

 HbA (22) is the most common – 96-98%.
 HbA2 (22) is the second most common – 1.5-3.2%.
 HbF (22) is the least common – 0.5-0.8%.

Question 23

How can we determine the different proportions of each haemoglobin in an adult

Answer 23

High performance liquid chromatography can seperate haemoglobins based on their electrophoretic charge and molecular mass
Different peaks= different Hb
HbF- to the left of HbA
HbA2- to the right of HbA

Each of these have a glycated fraction however only glycated HbA is normally present in sufficient quantity to be visible on a HPLC chromatogram and then only up to approximately 5%

Question 24

Describe the structure of globin

Answer 24

Primary
α 141 AA
Non- α 146 AA

Secondary
75% α and b chains-helical arrangement

Tertiary
Approximate sphere
Hydrophilic surface (charged polar side chains), hydrophobic core
Haem pocket (where haem component sits once four chains have assembled)

Question 25

Compare the structures of oxygenated and deoxygenated haemoglobins

Answer 25

§ Haemoglobin has the highest affinity to oxygen when the binding is loose (cooperativity) – more O2 means greater binding of O2.- O2 can access haem pocket

§ 2, 3-DPG is made by muscle cells (and other highly metabolising cells) to increase dissociation of oxygen
Configuration changes so that O2 cannot access haem pocket- squeezed out and delivered to tissues

Question 26

Ultimately, what does the oxygen-haemoglobin dissociation curve describe

Answer 26

O2 carrying capacity of Hb at different pO2

Question 27

What are the key features of the oxygen-haemoglobin dissociation curve

Answer 27

Sigmoid shape
Binding of one molecule facilitate the second molecule binding (cooperativity)- equally losing one O2 molecule makes it easier for other oxygen molecules to dissociate

P 50 (partial pressure of O2 at which Hb is half saturated with O2) 26.6mmHg- for HbA- approx 4kPa

kPa of O2 on the x-axis
HbO2 (%) on y-axis

Question 28

What does the P50 allow us to compare

Answer 28

The different affinities of different haemoglobin molecules for oxygen.

Question 29

What does the normal position of the dissociation curve depend on

Answer 29

Concentration of 2,3-DPG
H+ ion concentration (pH)
CO2 in red blood cells
Structure of Hb

Question 30

Describe the factors that lead to a right shift

Answer 30

Right shift (easy oxygen delivery)

High 2,3-DPG
High H+
High CO2
HbS

Question 31

Describe the factors that lead to a left shift

Answer 31

Left shift (give up oxygen less readily)
Low 2,3-DPG
HbF (important for fetus to have Hb with a greather affinity for oxygen than adult haemoglobin).

Question 32

What is meant by the T and R configurations of haemoglobin

Answer 32

Deoxyhaemoglobin exists in a tight (T) configuration and has a relatively low affinity for oxygen. Oxygen molecules are taken up sequentially by the 4 haem groups and at some point the partially liganded Hb molecule switches to a relaxed (R) configuration which has a markedly higher affinity for oxygen.

Question 33

Describe the axis of the dissociaiton curve

Answer 33

On the Y axis is the oxygen saturation which is defined as the fractional occupancy of the oxygen binding sites, and on the X axis is concentration of oxygen which is expressed as its partial pressure:

Question 34

Describe how affinity of haemoglobin changes with oxygen binding and how this helps its role of oxygen transport.

Answer 34

The more oxygen binds, the greater the affinity of the haemoglobin for oxygen.

This is good because if deoxyhaemoglobin has a low affinity for oxygen (as no oxygen is already bound), it will only pick up oxygen if the oxygen saturation is very high (i.e. in the lungs) so it will not take up oxygen in the metabolically active tissues where the oxygen saturation is low and where the tissues need oxygen.

Similarly, oxyhaemoglobin has a high affinity for oxygen so it will only give up oxygen in environments where the oxygen saturation is very low (i.e. respiring tissues that need oxygen)

Question 35

Describe the different parallel shifts of the ODC

Answer 35

The binding of oxygen by haemoglobin is regulated by specific molecules in its environment. H+ ions, CO2 and 2,3- diphosphoglycerate (2,3-DPG) all stabilize the T form of the oxygen molecule by forming H bonds and thus decrease the oxygen affinity of the molecule. This is represented on the oxygen dissociation curve as a shift to the right i.e a higher concentration of O2 is needed for maximum O2 saturation if the concentration of CO2, H+ ions or 2,3-DPG are high. Thus in metabolically active tissues where the concentration of H+ ions and CO2 are high, oxyhaemoglobin will assume the T configuration and give up oxygen readily.
Conversely in the lungs where CO2 is exhaled, oxygen affinity is higher. This effect of CO2 on the affinity of Hb for oxygen is called the Bohr effect.

Question 36

What effect does 2,3-DPG have on oxygen delivery

Answer 36

It facilitates oxygen delivery by making the haemoglobin molecule less flexible and pushing out the oxygen.

Question 37

How can we categerosie haemoglobinopathies

Answer 37

Structural variants of haemoglobin - mutation resulting in change in structure of haemoglobin- HbS
or
Defects in globin chain synthesis (thalassaemia)- quantitative defect in production of globin and thus haemoglobin

Question 38

Describe the key features of thalassaemia

Answer 38

Genetic disorders characterized by a defect of globin chain synthesis

Most common inherited single gene disorder worldwide

“thalassa” - sea“haimia” – blood disorder

Prevalent where malaria is also endemic- Hb variants offer protection against malaria

Question 39

Describe the classification of thalassaemias

Answer 39

§ Classification of thalassaemia:

o Globin type affected (alpha or beta gene cluster)

o Clinical severity:

§ Minor or “trait”.

§ Intermedia.

§ Major.

Major disorders- transfusion dependent for survival

Trait- carrier states- asymptomatic- but can pass on gene
Intermediate- wide spectrum of phenotype- dependent or non-dependent on transfusions

Better to classify as transfusion or non-transfusion dependent

Question 40

What is thalassaemia

Answer 40

Disorders in which there is a reduced production of one of the two types of globin chains in haemoglobin leading to imbalanced globin chain synthesis
The thalassaemias are disorders in which there is underproduction of one of the types of globin chains of adult haemoglobin and are called alpha or beta thalassaemia according to the chains affected.

Question 41

What can cause an underproduction of a globin chain

Answer 41

Globin genes are transcribed into messenger RNA which is processed before translation into protein. Underproduction of a globin chain may therefore result from deletion of part (or all) of the gene, or else genetic mutations which lead to defects in transcription, mRNA processing, translation or stability of the final protein product.

Different sets of mutations develop in different parts of the world. They probably arose independently and were expanded by selection, possibly in relation to malaria.

Question 42

Describe the psuedo genes found on the alpha cluster

Answer 42

There are 3 pseudo genes (w) and a fourth which although theoretically functional does not produce a detectable protein

Question 43

Summarise beta thalassaemia

Answer 43

Deletion or mutation in b globin gene(s)
Reduced or absent production of b globin chains
Prevalence – mainly Mediterranean countries (Greece, Cyprus, Southern Italy), Arabian peninsula, Iran, Indian subcontinent, Africa, Southern China, South-East Asia

Question 44

Ultimately, how is beta thalassaemia inherited

Answer 44

Beta Thalassaemia is inherited in a recessive mendelian fashion. The Carriers are asymptomatic save for the microcytic hypochromic indices. The clinical classification of Minor, Intermedia and Major shows how the mutations vary in severity. This can be explained by the degree of supression of globin chain sunthesis, some mutations result in no globin production (b0) where as others have decreased levels of production (b+). Inheritance of 2 b0 genes will give rise to a Major where as inheritance of 2 b+ genes will give rise to an intermedia (a clinically milder form)

Question 45

Give an example of how beta thalassaemia can be inherited

Answer 45

§ Inheritance:

o When 2 beta trait have a child, there is a 25% chance of a beta-major offspring.

o Beta Thal Intermedia can also come about when one partner has a beta+ mutation which is less severe.

§ b0 = deletion of one beta globin-encoding gene.

§ b+ = mutation of one beta-globin encoding gene.

Question 46

Describe the blood film findings of thalassaemia major

Answer 46

The main feature of thalassaemia is a microcytic hypochromic blood picture in the absence of iron deficiency. In addition to the microcytosis the RBC count is relatively high when compared to the haemoglobin.

The peripheral film shows hypochromia and target cells some poikilocytosis but no anisocytosis. (RDW is normal)

Question 47

Describe the findings of Hb electrophoretic studies in thalassaemia major

Answer 47

§ Hb EPS (electrophysiology studies)/HPLC (high performance liquid chromatography):

o a-thal – normal HbA2 and HbF, ±HbH.- makes it hard to diagnose alpha- thalassaemia using only Hb studies

o b-thal – raised HbA2 and HbF.

In beta thalassaemia the HbA2 is increased in relation to the severity of the mutation but is rarely above 7%.

Question 48

Describe the genetic studies for thalassaemia major

Answer 48

Globin Chain synthesis/ DNA studies
Genetic analysis for β-thalassaemia mutations and XmnI polymorphism (in β-thalassaemias) and α-thalassaemia genotype (in all cases)

Question 49

How can we diagnose the alpha thalassaemia trait

Answer 49

There is no simple diagnostic process to diagnose alpha thalassaemia trait
a presumptive diagnosis of a-thalassaemia trait can be made if microcytosis and hypochromia is seen in the absence of iron deficiency.

Question 50

What would a blood film with beta thalassaemia trait show and what are the features of beta thalassaemia trait

Answer 50

The blood film of a Beta thalassaemia trait will show microcytosis, hypochromia and occasional cells showing basophillic stippling
is a carrier trait and often asymptomatic.
§ Diagnosis usually made by blood film showing hypochromic microcytic blood cells and raised HbA2 and HbF
HbA still predominate (still have one functioning beta gene which can compensate)

Question 51

Summarise beta thalassaemia major

Answer 51

Carry 2 abnormal copies of the beta globin gene
Severe anaemia, incompatible with life without regular blood transfusions
Clinical presentation usually after 4-6 months of life

Question 52

What will the blood film of a patient with beta thalassaemia major show

Answer 52

The peripheral blood film will show extreme hypochromia, microcytosis and poikilocytosis.
Often Howell Jolly bodies and nucleated RBC’s will be present as a result of splenectophy and a hyper plastic bone marrow
Anaemia
In Beta thalassaemia major two forms of inclusion bodies may be seen, Alpha globin precipitates and pappenheimer bodies. If stained with Perls stain the inky blue granules aare demonstrated showing the papenheimer bodies to be haemosiderin granules.

Alpha globin chains are unstable and readily precipitate. These cause the cells to be more rigid and ineffect give alpha thalassaemia major its haemolytic component.

Question 53

Describe the clinical features of beta thalassaemia major

Answer 53

Beta Thalassaemia Major presents at 6-12 months of age as the synthesis of g globin chains is reduced and the b globin chains would be expected to be increasing toward normal adult levels but in the case of beta thalassaemia major the beta genes are supressed.
As a result of the gross anaemia the marrow becomes hyperplastic in an attempt to redress the anaemia. Should this persist the bome marrow expands giving rise to characteristic facial changes, frontal bossing and thikening og the maxillary bones
The patient will show splenomegally as extramedullary haemopoesis (erythropoesis outside the bone marrow) develops –reverts back to embryonic sites of haematopoiesis

Haemoglobin electrophoresis will show little or no HbA and increased levels of HbA2.

Question 54

List the clinical features of beta thalassaemia

Answer 54

Chronic fatigue
Failure to thrive
Jaundice- unstable Hb- chronic haemolysis
Delay in growth and puberty
Skeletal deformity
Splenomegaly
Iron overload

Question 55

List the complications of beta thalassaemia

Answer 55

Cholelithiasis and biliary sepsis (due to increased BR as  result of jaundice)
Cardiac failure (iron deposits)
Endocrinopathies (iron deposits)
Liver failure (iron deposits)

Question 56

Describe the importance of detecting beta thalassaemia major early

Answer 56

Patients with thalassaemia major usually present within the first year of life with failure to thrive, and general malaise. Splenomegaly and bony deformities of the skull are characteristic and bone changes in the long bones may be associated with recurrent fractures. Without transfusion the children usually die by the age of 7. If blood transfusions are commenced in infancy, however, then early growth and development may be normal. The blood transfusions are themselves associated with considerable morbidity due predominantly to iron overload but also as a result of the transmission of blood borne viruses (e.g. hepatitis B and C and HIV). Each unit of blood contains 200 mg iron and this accumulates in the liver, heart and endocrine glands. The effects of this start to appear by the end of the first decade.

Question 57

Why does the bone marrow enlarge in patients with beta thalassaemia

Answer 57

Cells which do manage to mature and enter the circulation contain β-chain inclusions and are removed by the spleen which subsequently enlarges. The anaemia stimulates erythropoietin production and this causes expansion of the bone marrow in the skull and long bones.

Question 58

Describe the endocrinopathies associated with beta thalassaemia major

Answer 58

Secondary sexual development may be delayed or absent, the normal adolescent growth spurt fails to occur and diabetes, hypoparathyroidism and adrenal insufficiency may become apparent. In addition, progressive liver and cardiac damage occur and liver damage from the iron overload may be exacerbated further by infectious hepatitis. Death usually occurs before the age of 25. Removal of iron is difficult.

Question 59

Describe the pathogenesis of beta thalassaemia

Answer 59

There is death of red cells in the marrow because of ineffective erythropoiesis
The removal of red cells by the spleen causes:
· Large spleen
· Anaemia
· Increased EPO
· Expansion of bone marrow

Question 60

What are the most common causes of deaths in patients with beta thalassaemia

Answer 60

240 Thalassaemia major patients born in Italy between 1960 and 1984
Cardiac disease		71%
Infections		12%
Liver disease		6%
Other causes 		11%

US cohort (Cooley’s Anemia Foundation) 11% of 724 registered patients died from Jan 1999 to July 2008
Cardiac			42 (54%)
Infections 		5

Question 61

List the treatments for beta thalassaemia major

Answer 61

Regular blood transfusions
Iron chelation therapy
Splenectomy (very symptomatic or high transfusion requirement)
Supportive medical care
Hormone therapy
Hydroxyurea to boost HbF
Bone marrow transplant (only curative measure)

Question 62

Explain the need for iron chelation therapy

Answer 62

Toxicity of iron overload- organ toxicity etc

Iron chelation- stop iron overload
Transfusion dependent- major cause is blood transfusions (iron burden)
Non-transfusion dependent- due to increased gut absorption- iron dysregulation- hepcidin (negative regulatory effect on iron)- downregulated- increased uptake of iron from G.I tract

Question 63

Describe the features of transfusions to treat beta thalassaemia major

Answer 63

Phenotyped red cells (match blood groups to prevent hallo-immunisation)
Aim for pre-transfusion Hb 95-100g/L (to reduce risk of extra-medullary haematopoiesis)
Regular transfusion 2-4 weekly
If high requirement, consider splenectomy

Question 64

Describe infection management in patients with beta thalassaemia major

Answer 64

Yersinia
Other Gram negative sepsis (Klebsiella)

Prophylaxis in splenectomised patients – immunisation and antibiotics

Splenectomy- at risk of infections from encapsulated bacteria

Infections from organisms which thrive on Fe

Question 65

Summarise the features or iron chelation in patients with beta thalassaemia major

Answer 65

Start after 10-2 transfusions or when serum ferritin >1000 mcg/l
Audiology and ophthalmology screening prior to starting

Question 66

What have studies demonstrated about iron chelation therapy

Answer 66

Many years of clinical and research experience have improved knowledge of management of iron overload and how to achieve effective chelation therapy
Achievement of continuous chelation coverage is an essential characteristic of effective chelation therapy. Constant, 24-hour control of NTBI/LPI protects against the harmful effects of toxic iron and helps to prevent further tissue damage
Good treatment compliance is important in achieving chelation coverage has been shown to be a key factor in attaining therapeutic efficacy and improving morbidity and survival

Question 67

What determines survival in patients with iron chelation therapy

Answer 67

Compliance with desferrioxamine(DFO) therapy determines survival

Compliance with this drug an issue- infusion period of 12 hours- stigma and burden on life

Deferiprone and deferasirox are administered orally, which eliminates a major hindrance to chelation therapy with desferrioxamine – the necessity for delivering the agent subcutaneously or intravenously over an extended period of time using specialized pumps. To date the indication of deferiprone is restricted to second line in Europe.

Question 68

Describe Deferasirox (Exjade)

Answer 68

Oral (once daily)
Dose 20-40mg/kg
SE: rash, GI symptoms, hepatitis, renal impairment 
Faecal exretion
Half-life of 12-16 hours

Limited clinical experience

Question 69

Describe Desferrioxamine (Desferal)

Answer 69

Long-established
Sc infusion 8-12 hours 5-7 days per week (or IV in cardiac iron overload)
Dose 20-50 mg/kg/day
SE: vertebral dysplasia, pseudo-rickets, genu valgum, retinopathy, high tone sensorineural loss, increased risk of Klebsiella and Yersinia infection
Compliance
Vitamin C

Urinary and faecal excretion
Half-life of 20-30 minutes

Question 70

Describe Deferiprone (Ferriprox)

Answer 70

Licensed 1999
Oral (3 times daily)
Dose 5-100 mg/kg/day
Effective in reducing myocardial iron
SE: GI disturbance, hepatic impairment, neutropenia, agranulocytosis ( which can lead to sepsis), arthropathy

Need weekly blood counts to monitor neutropenia
Urinary excretion
Half-life of 3-4 hours

Question 71

What are the advantages and disadvantages of Desferrioxamine

Answer 71

Advantages:
Three decades experience	
			Survival benefit 	                
			Heart failure prevented         
			and reversed 	                    

Disadvantages:
Paraenteral administration- limits compliance
Toxicity (dose dependent)
Ocular
Skeletal
Auditory

Question 72

What are the pros and cons of Deferiprone

Answer 72

Advantages:
Oral
Cardioprotective

Disadvantages:
	3 x/day  7days/week
			                 Short plasma t 1/2
						Unpredictable control of 
                                                                                  body  iron
                                                                                 Toxicity
						     - Agranulocytosis(~0.5%)
						     - Arthropathy
						     - Zinc deficiency

Question 73

What are the pros and cons of Deferasirox

Answer 73

Pros:
oral
control of body iron
specific
once daily

cons:
Cardiac protection uncertain
Limited clinical experience
Toxicity limited but long term data lacking

Question 74

Describe the benefits of combination therapy in iron chelation

Answer 74

To limit side effects and toxicity- can reduce dose

Question 75

When is bone marrow transplantation an option

Answer 75

Bone marrow transplantation has the potential to cure thalassaemia major and should be considered in transfusiondependent thalassaemics under the age of 16 years who have an HLA-identical sibling greater than 18 months of age.

Question 76

Outline how we can monitor for iron overload

Answer 76

Serum ferritin
>2500 associated with significantly increased complications
Acute phase protein
Check 3 monthy if transfused otherwise annually

Liver biopsy
Rarely performed

T2* cardiac and hepatic MRI
<20ms – increased risk of impaired LF function
Check annually or 3-6monthly if cardiac dysfunction

Question 77

Describe the ferriscan for monitoring iron overload

Answer 77

Ferriscan – R2 MRI
Non-invasive quantitation of LIC
Not affected by inflammation or cirrhosis
<3mg/g normal
>15mg/g associated with cardic disease
Check annually or 6monthly if result >20

Question 78

Describe sickle beta-thalassaemia

Answer 78

§ Thalassaemia mutations can be co-inherited with other complications – such as SCD and beta-thal.
§ Co-inherited Beta-Thal:
o Sickle Beta Thalassaemia.
o HbE Beta Thalassaemia – very common in SE Asia and can be as severe as beta-thal major.

The blood film shows all the features of both sickle and beta thalassaemia, sickled cells, target cells, microcytosis and hypochromia. As little or no HbA is being produced in these patients HbS will be the dominant haemoglobin and will precipitate as it does in homozygote sickle cell patients

Question 79

Describe HbE beta-thalassaemia

Answer 79

HbE b-thalassaemia: globin chain of HbE unstable, so similar to b-thalassaemia intermedia
Very common combination in South East Asia
Clinically variable in expression can be as severe as thalassaemia major

Question 80

Explain the features of HbE beta-thalassaemia

Answer 80

In south east asia where both beta thalassaemia and HbE are found, HbE Beta thalassaemia is common.. The globin chain of HbE is unstable and hence at a molecular level this can be classed as a mild form of beta thalassaemia. Hence coinheritance of Beta Thalassaemia Trait. In terms of clinical severity it is classed as a Beta Thalassaemia intermedia. However the degree of clinical support required by such individuals varies quiet markedly.

Question 81

What is the outcome of alpha thalassaemia major

Answer 81

Fatal in utero because alpha globin is needed to make HbF (alpha + gamma

This is why only up to 3 alpha genes can be affected in adult

Question 82

Describe the features of alpha thalassaemia

Answer 82

o Due to a deletion or mutation in alpha globin genes – reduced or absent alpha globins.
o Affects both foetus and adult (alpha is in ALL globin variants).
o Severity depends upon number of chains affected.
o Excess beta and gamma chains will form tetramers of HbH (beta excess) and HbBarts (gamma excess).

Question 83

What is meant by a thalassaemia carrier

Answer 83

Also known as Thalassaemia minor / trait
Carry a single abnormal copy of the beta globin gene
Usually asymptomatic
Mild anaemia 
Usually low MCH and low MCV

Question 84

Describe HbH disease

Answer 84

Loss of 3 alpha chains
Severe anaemia
Non-transfusion dependent
Cells still well haemoglobinised

The peripheral blood film of HbH disease has a haemolytic element to it with microcytosis, anisoocytosis poikilocytosis and “puddling” of haemoglobin within the RBC.

Hb Electrophoresis shows a fast band which is probably more easily seen shortly after the strip has started to run.

The amount of Hb Barts seen in the neonate does not directly correleat with the amount of HbH present in the adult

Question 85

Describe the different types of alpha thalassaemia

Answer 85

Alpha chains are found in HbA and HbF so alpha thalassaemia may present clinically in utero. Alpha thalassaemia is usually (>80% cases) due to a deletion of one or more alpha genes and since each alpha cluster (one on each chromosome) has two alpha genes, four syndromes are possible as follows each with an increasing degree of anaemia and associated morbidity: α+ trait where one locus fails to function, α0 trait where two loci on the same chromosome are dysfunctional, HbH disease with three loci affected and Hb Bart’s hydrops fetalis where all four loci are defective and death in utero is the norm. α+ thalassaemia is particularly common in Africa and in those of African descent and α0 thalassaemia is particularly common in SE Asia.

Question 86

Describe the features of heterozygotes for A+ and Ao thalassaemias and explain how we can distinguish the two

Answer 86

Someone who is heterozygous for alpha+ thalassemia will still have 3 functioning alpha globin genes so they will only be mildly anaemic
n the heterozygous state there are still 2 functioning alpha globin genes so they will also only experience mild anaemia

Most people with alpha 0 thalassemia have a MCH < 25 pg

Question 87

What could be the potentially devastating consequences for someone with mild anaemia caused by alpha 0 thalassemia?

Answer 87

Someone with alpha 0 thalassemia may not experience any symptoms themselves, but if they try and have a child with someone who also has alpha 0 thalassemia then there is a chance that their child may not have any functioning alpha genes (haemoglobin barts).

Question 88

What are the problems associated with treatment in developing countries

Answer 88

Lack of awareness of the problems
Lack of experience of health care providers
Availability of blood
Cost and compliance with iron chelation therapy
Availability of and very high cost of bone marrow transplant

Question 89

Describe screening and prevention techniques

Answer 89

Counselling and health education for thalassaemics, family members and general public
Extended family screening
Pre-marital screening?
Discourage marriage between relatives?
Antenatal testing
Pre-natal diagnosis (CVS

The success of prevention programs in Cyprus and Italy, for example, resulted by the mid-1980s in the dramatic reduction of the number of affected births, plummeting to almost zero in Cyprus by 1986

Question 90

What is the main cause of the pathophysiology of beta thalassamia

Answer 90

The surplus of alpha globin chains form tetramers.
These alpha globin tetramers precipitate in the bone marrow, which leads to ineffective erythropoiesis and haemolysis in the peripheral circulation

Question 91

Summarise the features of the beta thalassaemia trait

Answer 91

Heterozygotes for a beta thalassaemia gene are said to have β thalassaemia trait. These carrier states are usually clinically silent, and can be referred to as thalassaemia minor. They can, however, be identified in the laboratory on the basis of abnormal red cell indices. Typically, patients with β thalassaemia trait have smaller red cells than usual (microcytosis) and a reduced mean cell haemoglobin (MCH) with a normal mean cell haemoglobin concentration (MCHC).
The red cell count is usually raised and the haemoglobin level is normal or slightly reduced. If β thalassaemia trait is suspected then the level of HbA2 should be measured and is typically raised. If levels are equivocal even on repeat testing, and there is no evidence for coexisting iron deficiency then DNA analysis could be considered.

Question 92

Why is it important to identify patients with the beta thalassaemia trait

Answer 92

There are two situations in which identifying patients as having β thalassaemia trait is of value. Firstly, the microcytosis may be misinterpreted as iron deficiency if the raised red cell count and normal MCHC are not noted.
If these patients are then put on long term iron they can become iron overloaded. Secondly, it is important to identify pregnant patients with thalassaemia trait so that their partners can be tested and the couple can be counselled about their chance of having a baby with clinically significant thalassaemia and can be offered further testing.

Question 93

Describe the genetic background of beta thalassaemia

Answer 93

Genetic background: b-thalassaemia is recessive autosomal, with asymptomatic carriers
Mutations: can be b0 where no globin is produced or b+ where production is decreased
Possible combinations: bb0/bb+ thalassaemia trait; b0b0 thalassaemia major; b0b+ thalassaemia intermedia

Question 94

Describe the mutations responsible for alpha and beta thalassaemias

Answer 94

Alpha thalassemia – deletion

Beta thalassemia – point mutation (over 100 described)