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Haematology > CH4-6 > Flashcards

CH4-6 Flashcards

1
Q

What is haemoglobinopathy?

A

Haemoglobinopathy is a kind of genetic defect that results in abnormal structure of one of the globin chains of the hemoglobin molecule.

Hemoglobinopathies are inherited single-gene disorders; in most cases, they are inherited as autosomal co-dominant traits

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2
Q

Give examples of common haemoglobinopathies

A

Sickle Cell Disease

Thalassaemia

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3
Q

What are the common clinical symptoms of haemoglobinopathy?

A

Anaemia (with sickle cell disease, but not in carriers as they are asymptomatic)

Pallor of the skin (poss. due to anaemia)

Jaundice (due to high bilirubin)

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4
Q

How are haemoglobinopathies transmitted?

A

It is a mono-genetic disorder

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5
Q

How are clinically significant haemoglobinopathies treated?

A

Iron - only if they are anaemic
Multivitamins - There is a chance they may be slightly deficient in B12 and folic acid, so are not producing new effective cells
Blood transfusion therapy - to reduce some of the symptoms in severe patients, and will also reduce the incidence of patients have a stroke.

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6
Q

What are the side effects of blood transfusion therapy?

A

Patients can develop antibodies, and so can no longer have transfusions

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7
Q

How do haemoglobinopathies effect the red cell?

A

Life span is reduced from ~120 days, to 15-20 days

Cells are smaller, so greater percentage of cell in occupied by Hb (normally 30% of cell), making the cell less flexible as there is less fluid content

Biconcave shape lost

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8
Q

What is the function of Hb?

A

It is to transport O2 and CO2.

In something with Hbopathy, they are always hypoxic and short of breath

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9
Q

What are the 2 types of haemoglobin?

A

Hb and myoglobin (found in the muscles).

The myoglobin is Hb with a higher oxygen affinity.

The arteries carrying normal Hb will have the oxygen stripped when it passes the Mb in the muscles.

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10
Q

How does sickle cell disease effect the Oxygen Saturation Curve?

A

In patients with sickle cell, their OSC will be the right of a normal curve.

Treatments for Hbopathy is to correct this curve

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11
Q

What are the different types of disorders found in haemoglobinopathies?

A

Quantitative Disorder – the production (quantity of Hb is reduced leading to anaemia

Qualitative disorder – the quantity of Hb is normal, but the type is abnormal.

Some patents can have the genetic defect that affects the quantity and also inherit the defect that affects the quality of Hb produced and this is called compound heterozygous or compound homozygous (depending upon what is inherited).

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12
Q

Give examples of clinically significant Hbopathies

A 
• Hb S
• Hb C
• Hb D
• Hb E
• Hb O Arab
• Hb Lepore
• Thalassaemias
• Compound heterozygotes
eg Sickle/beta thalassaemia
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13
Q

What is the most common Hbopathy around the world?

A

Alpha Thalassaemia

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14
Q

How many people are carriers of Hbopathy?

A

5% of the world population

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15
Q

Describe the epidemiology of Hbopathies

A
  • Annual affected birth 300,000
  • Of which 70,000 born with beta thal major
  • 1.5% world population – carrier of beta thal (80-90 million people).
  • 7% world population carriers of Hb variants.
  • 250 million carrier alpha+ beta thal carrier
  • HbS 20% - Africa
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16
Q

What complications can occur by having Hbopathy?

A

Polymerisation (especially in the homozygous form) – Hb polymerises in the red cell, this is how the cell shape changes to sickle shape.

Haemolysis leading to anaemia

Altered oxygen affinity (relating to the oxygenation curve)

Methaemoglobinaemia. (Fe3+) non-functional Hb causes decrease O2 to tissue leading to cyanosis.In this state it is no longer able to transport oxygen, leading to a reduction in the tissues and cyanosis.

Thalassaemia syndromes

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17
Q

Describe the genetic features of Sickle Cell disease

A

• Mutation of a single nucleotide from a GAG to GTG codon mutation - glutamic acid replaced by valine
• Under conditions of low O2 concentration, cause polymerization of the HbS
• Valine – formation of hydrophobic contacts between
valine of one HbS and alanine, phenylalanine, leucine
from adjacent Hbs
• Fibres stretch and deform the red cells

Once it is in the polymerised form, it cannot go back. In a normal healthy cell, the Hb is soluble. In patients with homozygous form, after a cycle of oxygenation, deoxygenation and polymerisation, the cell becomes stiff and it is this that causes all the problems with this disease.

It alters the rheology of the red cell (the flow).

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18
Q

How is Sickle Cell disease inherited?

A

Autosomal recessive inheritance

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19
Q

Where is Sickle Gene found?

A

Chromosome 11

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20
Q

How is sickle cell classified?

A

Sickle cell anaemia - Hb SS - major condition
Sickle cell trait - Hb AS - generally asymptomatic
Hb SC disease - clinically significant condition
Hb S/β0 thalassaemia - significant disease
Hb S/β+ thalassaemia - less problematic

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21
Q

Describe the pathophysiology of Sickle Cell disease

A

• Single point mutation causes base substitution in the β chain, position 6 - Glutamic acid replaced by Valine

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22
Q

How does the effect of deoxygenation occur in sickle cell?

A

• In the deoxygenated state, forms 14 member fibres
• Critical nucleus of 10 molecules → fibre formation.
• Rate of polymerisation is affected by conc. of deoxygenated HbS to the power of 10.
• In sickle cell trait there is half conc. of deoxygenated HbS ∴ rate is 2^10 = 1024 times slower.
• Causes vascular occlusion of small and large vessels –
leading to chronic damage of multiple organs.

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23
Q

How does HbS polymerisation affect the blood?

A

Sickle cells can initially move through the capillaries, but after polymerisation, they are rigid and cannot travel through the capillaries via tank treading and so block the area around the capillaries, causing cyanosis and possibly and infarction.

Due to the shape they also alter the viscosity of the whole blood, so it all moves more slowly through the body. The red cells are dehydrated, but because they lose more K+and Ca2+, they also lose water and become smaller.

The process of oxygenation, deoxygenation and polymerisation produces cells that cannot change and results in microvascular occlusion and premature red cell destruction. The bone marrow is constantly active to try to compensate for the anaemia.

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24
Q

How does sickle cell affect the patient?

A

Results in microvascular occlusion and premature red cell destruction, leading to chronic severe haemolytic anaemia

Compensation - ↓ O2 carrying capacity,↑ plasma volume,
↑ CO and enlarged heart.

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25
Q

What is tank treading?

A

Tank treading is how red cells move. They move round and are flexible (70% fluid) and therefore able to travel through the 3 micron capillaries, by being able to squash down.

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26
Q

What are the features of SCD?

A
  • Polymerization
  • Loss of deformability
  • Increase cell adhesion
  • Haemolysis
  • Vaso-occlusion
  • Painful crisis
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27
Q

Describe the ethnic distribution within the UK of SCD

A
  • African 1:4
  • West Africans, Caribbean 1:10
  • Asian 1:50
  • Mediterranean 1:100
  • Middle East 1:100
  • Others: all areas of the new world whose ancestors have migrated from above areas

In UK > 12,500 people with SCD
100 – 150 neonates are born with SCD per annum

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28
Q

Describe the features of Sickle Cell Trait

A
  • Benign
  • Asymptomatic
  • Electro- A/S band, HbS 25-45%
  • Immune to malaria
  • Carry a genetic risk to their offspring
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29
Q

How is SCD related to malaria?

A
  • In a carrier, the presence of the malaria parasite causes the red blood cell to rupture, making the plasmodium unable to reproduce.
  • Polymerization of Hb affects the ability of the parasite to digest Hb in the first place. Therefore, in areas where malaria is a problem, people’s chances of survival actually increase if they carry sickle cell trait (selection for the heterozygote).

It is possible that the trait came about as an evolutionary change to give immunity to malaria, therefore improving survival rates.

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30
Q

What are the characteristics of SCD?

A

• Chronic haemolytic anaemia
- Rapid red cell destruction - jaundice
• Micro-vascular occlusion – infarction
- (excessive presence of N-methyl D-aspartate receptors – increase calcium uptake)
• Recurrent episodes of infection (

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31
Q

What problems can sickling cause?

A
  • Kidney disorder
  • Joint Disorder
  • Stroke
  • Retinal damage
  • Liver damage
  • Spleenic atrophy
  • Priapism
  • Leg ulcers
  • Chronic lung disease
  • Analgesia – addiction, tolerance and dependence (due to intense pain)
32
Q

What effect can sickling have on the different parts of the body?

A

• Cerebral – stroke, PE
• Ophthalmic – retinopathy HbSC > HbSS
Cardiovascular – PE, chronic leg ulcer,
• Respiratory – PE
• Gastro-intestinal, Gall-bladder - Gall stones
• Musculo-skeletal – “PAINFUL CRISIS”
- Intermittent episodes or crises - bone pain
- hand and foot syndrome (dactylitis)
- Long bones longer than normal
• Spleenic sequestration
• Anaemia

33
Q

What precipitating factors occur in people with SCD?

A
  • Infection
  • Exposure to extreme temperatures
  • Hypoxia
  • Strenuous exercise
  • Dehydration
  • Emotional Disturbances
  • Pregnancy
34
Q

How does SCD effect infection?

A

• Most common cause of death in children but a major problem at all ages
• Due to spleenic dysfunction from sickle damage
• Occurs from a few months of age especially with certain bacteria
– eg. Pneumococcal sepsis : 400 x ↑ risk
• Infection may be rapidly overwhelming

35
Q

How is infection prevented and treated in patients with SCD?

A 
Prevention:
– education
– Penicillin from 3/12 age
– Pneumococcal, HiB, Meningococcal vaccines
– malaria travel prophylaxis

Aggressive treatment of infections with high doses of antibiotics

36
Q

What are the features of strokes related to SCD?

A
  • Risk approx 1% per year ( > 280 x normal)
  • Peak incidence age 8
  • May result in physical disability, IQ reduction, learning difficulties, seizures
  • Monitoring for high risk and strategy for prevention is possible but relies on intensive transfusion programmes
  • After the age of 8, hospitals try to ensure the Hb levels are over 100.
37
Q

What are the lab findings associated with SCD?

A
  • Anaemia, Hb 6-10 g/dl
  • Retic 10-20%
  • Sickle cells
  • Target cell (Due to excessive dehydration or additional alpha or beta chains)
  • Howell-Jolly bodies
  • Nucleated RBCs
  • HbS - ↓ oxygen affinity
  • Red cells contain 80% HbS + HbF
  • Variable haemolysis

These patients are active and work with low levels of Hb, whereas someone without SCD, would be unlikely to be able to function at these levels.

38
Q

What complications can arise from SCD?

A
  • Hand and foot syndrome
  • Painful crises
  • Aplastic crises-marrow hypoplastic
  • Spleen/hepatic sequestration crises
  • Lung or brain syndrome-sickling
  • Infection eg Strep.pneumoniae, haem.influenzae
  • Gall stone
  • Progressive renal failure
  • Chronic leg ulcer
  • Recurrent priapism
  • Aseptic necrosis humoral/femoralhead
  • Chronic osteomyelitis.
39
Q

Why do patients with SCD experience constant bone pain?

A

Bone Marrow Expansion

The bone marrow is a factory for red cell production. In the slide occlusion/blockage has taken place, so this area has become dead.

The blood vessels are formed around the infarcted area and so the bone produces more bone marrow and so the bone elongates to store the new bone marrow.

This is why these patients experience constant bone pain (continual occlusion and bone expansion)

40
Q

What tests are performed to detect sickle cell?

A 
• Sickle test – positive
• Confirmation of AS/SS/SC
• Electrophoresis -cellulose 
                              -agarose gel
• IEF
• HPLC
• HbA2 - sickle/beta thal

If the sickle test is positive, it doesn’t tell you if the patient is a carrier or has the disease, so additional testing is required.

41
Q

How is SCD treated?

A
  • Prophylactic-avoid crises
  • Folic acid
  • Good general nutrition and hygiene
  • Pneumococcal vaccination
  • Oral antibiotics
  • During crises - rest, rehydrate, treat cause, analgesia, transfusion, exchange transfusion
  • Care in pregnancy
  • Blood transfusions
  • HbF – increase with hydroxycarbamide (HU) - and in combination with BTX – significantly decrease severity of painful crisis.
  • Iron chelation therapy.
42
Q

What is hydroxycarbamide (HU)?

A

Hydroxycarbamide is a new drug and is already used as a cancer drug and can significantly reduce the severity of the painful crisis.

43
Q

Why is HbF used in the treatment of SCD?

A

Hb F has a higher affinity for oxygen than normal Hb. It has a strong bond with oxygen and therefore does not enable the red cell to change to the sickle state, as there is always a small amount of oxygen in the cell (deoxygenation is needed for transfer to sickle state).

44
Q

How can SCD be prevented?

A
  • Ante-natal screening of all pregnant patients
  • If positive for HbS - Partner’s screening
  • Informed choice
  • Genetic counselling
  • Embryonic genetic testing

Following universal screening, hospitals have to report the result to the midwife within 3 days. This screening shows there is 25% of the child having the condition (trait or disease, depending upon the genetics of the father). The patient is asked to attend the hospital with their partner within one week, so they get all the information and are able to make an informed choice.

45
Q

What future treatments may be available for SCD?

A
  • Hydroxycarbamide or HU
  • BMT
  • Gene Therapy
  • Gene Correction

Problem:-
Limited availability
Currently very expensive

46
Q

What other variants can sickle cell be combined with?

A
  • Hb S/C
  • Hb S/D
  • Hb S/E
  • Hb S/thalassaemia
  • Hb S/HPFH
47
Q

What are the features of HbD Punjab?

A 
• Occurrence - Punjab region of India/Pakistan
• Pathophysiology
Glu→Glutamine (Gln) in beta chain at 121
• Clinical presentation -> homo - mild haemolytic anaemia
• FBC - Hb – 10 g/dl to normal
↑ RBC, low MCV and MCH
Retics 2 - 4%
• Blood film - target cells
• HPLC - normal Hb A2
and F levels
• Heterozygotes - asymptomatic with normal RBC
indices
48
Q

What are the features of HbE?

A
  • Occurrence - south east Asia, Thailand - 8 to 50-70%
  • Pathophysiology - Glu → lysine at 26 in beta chain
  • Clinical presentation
  • Homo - mild microcytic, hypochromic anaemia with target cells
  • FBC - Normal Hb, ↑ RBC, low MCV MCH, Normal Retics.
  • Blood film - hypochromia, microcytosis, occ. target cells
  • Heterozygotes - microcytosis
  • with +/- anaemia

If homozygous for this, you may have mild anaemia, but otherwise insignificant.

49
Q

What are the features of HbC?

A

• Occurrence - Ghana (up to 40%), American Negroes (2%)
• Pathophysiology - Glu → Lys at 6 in beta chain
• lower solubility than HbAA - crystallization - ↑ red cell
rigidity
• Clinical presentation - homo-mild haemolytic anaemia
• blood film - target cells , irregularly contracted cells
(spherocytes) and intracellular tetragonal crystals,
Occ. nucleated RBCs
• FBC - Hb ≅ 8g/dl, low MCV and MCH

50
Q

What are the feature of HbC trait?

A
  • Asymptomatic
  • Anaemia +/-
  • Normal FBC and indices
51
Q

What is thalassaemia?

A

• A group of inherited disorders resulting in reduced production of one or more globin chains
• This results in an imbalance of globin chains with the excess chain producing the pathological effects:
– damage to red cell precursors → ineffective red cell production
– damage to mature red cells → haemolytic anaemia
• Always results in hypochromic, microcytic anaemia

52
Q

What are the differences between alpha and beta thalassaemias?

A

• Genetic disorder resulting in reduced synthesis of normal α or β chains of Hb
– Either alpha chain defects – alpha thalassaemias
• 4 genes, 2 from each parent,
– Or beta chain defects – beta thalassaemias
• 2 genes, 1 from each parent
• Results in excess of opposite globin chain (i.e. either α or β)

53
Q

What causes thalassaemia?

A
  • Gene Deletion - mainly lead to alpha thal partial (alpha+) or complete abolish (alpha0) thalassaemia.
  • Point Mutation mainly occur in beta thalassaemia leading either to partial (beta+) or complete absence of beta globin (beta0)
54
Q

What mutations cause beta thalassaemia?

A
  • Transcriptional mutants – promoter elements
  • RNA Processing – splice junction, Consensus splice sites
  • RNA translation - initiation codon, nonsense codons, frameshift mutation
55
Q

What are the different classifications of thalassaemia?

A

Major. This is the clinical disease form and there is a total absence of one of the globin chains (alpha or beta).

Intermediate. This is an in-between type.

Minor. This is the trait/carrier/heterozygous form. You have some production of the globin chain.

56
Q

How prevalent are thalassaemia carriers in the UK?

A 
• Alpha thalassaemia
– Chinese –1 in 15 to 1 in 30
– Cypriots –1 in 50 to 1 in 300
• Beta thalassaemia
– Cypriots – 1 in 7
– Asians – 1 in 10 to 1 in 30
– Chinese – 1 in 30
– Afro Caribbeans – 1 in 50
– White British – 1 in 1000
57
Q

What are the clinical features of beta thalassaemia major?

A 
Severe anaemia from 3-6 months after birth
Vomiting feeds
Failure to thrive
Irritability
Sleepy
Shortness of breath
Shortness of growth
Stunted growth
Enlarged spleen and liver
Vitamin-D deficiency
58
Q

What are the clinical features of thalassaemia in adults?

A
  • ↑ liver and spleen size
  • ↑ RBC destruction → iron overload
  • Bone changes due to marrow hyperplasia → tendency to fractures
  • Transfusion → iron overload, damage to liver, endocrine organs, myocardium
  • Infection-related to iron overload, and treatment
  • People tend to have a round face, similar jawlines and few hairs on their face in adulthood.
  • Large liver and spleen full of trapped abnormal blood cells. The treatment may be removal of the spleen.
59
Q

What are the laboratory diagnostic details for thalassaemia?

A

• FBC-micro, hypochromic
• ↑ Retic,
• Blood film-target cells, basophilic stripping
• Electrophoresis - HbA absent or v.absent
• Col. chromatography/HPLC HbA2 (2-8%)
• Bertke method/electro/HPLC-HbF (98%)
• α/β ratio ↑, little or no beta chain production
• DNA analysis-identify carriers & prenatal screen
• Assessment of iron status
- serum ferritin and serum total iron
- TIBC and % TIBC saturation
- Excretion of iron in response to desferioxamine

60
Q

What is the life expectancy for individuals with Thalassaemia major?

A

• Without regular transfusion
– Less than 10 years
• With regular transfusion and no/poor iron chelation
– Less than 25 years
• With regular transfusion and good iron chelation
– 40 years, longer??

61
Q

How is thalassaemia treated?

A
  • Transfusion regime Hb > 10.0 g/dl, 2-3 RCC (white cell depleted) / 4 weeks
  • Splenectomy ≈ 6 years old - reduces transfusion due to ↓ removal of RBC
  • Folic acid if poor diet
  • Iron chelation therapy - desferioxamine, infusion method
  • Vitamin C - increase iron excretion
  • Vitamin E - improve antioxidant capacity
  • Endocrine therapy
  • Hepatitis B immunisation
62
Q

What is the role of the spleen?

A
  • Production of Lymphocytes (WBC)
  • Filtration of waste products
  • Destruction of old or damaged erythrocytes (RBC)
63
Q

Why is iron chelation therapy required by all patients receiving regular blood transfusions?

A

Iron overload can kill the patient if untreated. If we have surplus/excess iron, the only way we can get rid of it is via normal gut bleeding that happens every day.

When there is far too much, this is toxic to the heart, results in increased infection and will also increase the chance of stroke. Iron chelation therapy is therefore needed (e.g. desferioxamine) by these patients.

64
Q

What complications can occur in patients receiving regular blood transfusions?

A 
• IRON OVERLOAD
Multi-organ failure
– Endocrine organs
      - Growth failure
      - Thyroid failure
      - Gonadal failure - infertility
– Cardiac
– Liver
65
Q

How is thalassaemia major cured?

A

• Bone Marrow Transplant

In children, success rate of 80%, mortality 5-10%

66
Q

What are the features of thalassaemia minor?

A
  • Benign - Asymptomatic
  • ↓ MCV ( 3.5%
  • Normal iron unless IDA
  • Often confused with Fe deficiency due to reduced MCV and MCH
67
Q

What are the features of thalassaemia intermedia?

A
  • Mild defect in β or α chain synthesis

* Reduction of globin chain imbalance by interaction of α thal with β thal.

68
Q

What are the features of compensatory γ chain synthesis?

A

Compensatory γ chain synthesis
• Associated with hereditary persistence of foetal haemoglobin (HPFH)
• δβ thal or HPFH due to deletions or other modifiers of γ chain activity
• Proteolysis of excess globin chains

69
Q

What are the clinical features of compensatory γ chain synthesis?

A
  • Hb 7-10 g/dl
  • Require transfusion
  • May show bone deformities
  • Splenomegaly
  • Iron overload due to ↑ absorption
70
Q

Why are haemoglobinopathies screened for?

A

It’s no good treating someone for something until you know what they have, as you may give the wrong treatment, or giving treatment when it isn’t required.

Also, you can alleviate the complications by screening.

71
Q

What types of screening is available to detect Hbopathies?

A 
• Newborn
• Adolescence
• Premarital
• Preconception
• Antenatal
• Foetal sample for Hb disorders
Chorionic Villus sample (CVS), > 11 weeks
Amniotic fluid sample, 15 –19 weeks
Foetal blood sampling
Non invasive prenatal diagnosis through foetal DNA or
foetal cells in maternal circulation
72
Q

What laboratory tests can be performed to detect haemoglobinopathies?

A
  • Sickle solubility test
  • Electrophoresis - cellulose, alkaline and acid
  • Micro-column - HbA2
  • HPLC
  • HbF - alkaline denaturation (Betke method)
  • Capillary electrophoresis
  • Immunoassay
  • Mass spectrometry
  • DNA – PCR
  • Globin chain electrophoresis
73
Q

How is sickle cell solubility test performed?

A
  • Principle:- Deoxygenated HbS is insoluble in concentrated phosphate buffer
  • Buffer - (KH2PO4, K2HPO4, Saponin, Sodium dithionite)
  • Method: 3.0ml buffer + 100µl Whole Blood, incubate at 37oC for 5mins
74
Q

What do the results of the sickle cell solubility show?

A
  • Opaque (turbid) - positive for Hb S
  • Clear - negative
  • Centrifugation - HbS ring at the top
  • Negative clear purple solution with a thin ‘scum’ of precipitated protein and red cell stroma

• False positive - red cell debris, polycythaemia, increased paraprotein, unstable haemoglobin.
Correction - washed red cells.

• False negative - deterioration of the dithionite, unstable saponin, anaemia, post transfusion.

75
Q

What are the advantages of isoelectric focusing?

A
  • Separate more Hbs
  • Quantified with densitometry
  • Sharper bands
  • Separate HbD and G from S
  • Require small samples e.g. suitable for neonatal Hbop screening
76
Q

What are the disadvantages of isoelectric focusing?

A
  • Quantification at low concentrations have low precision
  • Not suitable for HbA2 assessment
  • Expensive both capital and running cost

Haematology (12 decks)

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