Haematology JC048: Family History Of Anaemia: Inherited Causes Of Anaemia, Haemolytic Anaemia, Aplastic Anaemia

Question 1

Haemolytic anaemia

Answer 1

• Anaemias which result from ↑ Rate of destruction of circulating RBC
• Compensatory ↑ Production from BM (if BM reserve is adequate)

Classification:
- Hereditary vs Acquired
- Intrinsic vs Extrinsic

Question 2

Hereditary / Inherited Haemolytic anaemia

Answer 2

ALL **Intrinsic
1. **Membranopathy
- Hereditary spherocytosis

2. ***Enzymopathy
   - G6PD deficiency
   - Pyruvate kinase deficiency
3. ***Haemoglobinopathy
   - HbS (sickle cell anaemia), HbH, Unstable haemoglobinopathy

Question 3

Acquired Haemolytic anaemia

Answer 3

Mostly ***Extrinsic except Paroxysmal nocturnal haemoglobinuria

Intrinsic RBC defect:
1. Paroxysmal nocturnal haemoglobinuria (PNH)
- **PIGA gene mutation —> deficiency of glycophosphatidylinositol (important for anchoring cell surface protein **CD55, CD59) —> deficiency of CD55, CD59 —> complement mediated lysis of RBC (Intravascular haemolysis)

Extrinsic factors causing RBC damage:
1. Immune
- **Autoimmune (due to AutoAb)
- **Alloimmune
—> Transfusion reactions
—> Haemolytic disease of newborn
- **Drug-induced (e.g. **Methyldopa, some antibiotics)

2. Heat, venoms, chemicals damaging RBC membrane
3. Drugs, chemicals oxidising Hb and other cellular components
4. Red cell fragmentation syndromes
   - **MAHA (e.g. TTP)
   - **Mechanical haemolytic anaemia (e.g. Mechanical heart valves)
5. Induced by microorganisms
   - Bacterial infection of RBC (e.g. Clostridium perfringens)
   - ***Parasitic infection of RBC (e.g. Malaria)

Question 4

***History taking of Haemolytic anaemia

Answer 4

1. Family history
2. Ethnicity (e.g. **sickle cell anaemia in black, **thalassaemia in SE Asian)
3. Infection (e.g. ***malaria)
4. Drugs
5. Transfusion history
6. Co-existing illnesses e.g. ***Autoimmune diseases, Lymphoproliferative neoplasm
7. History of ***gallstone (∵ longstanding haemolysis)

Question 5

***Clinical features of Haemolytic anaemia

Answer 5

1. Pallor
2. ***Jaundice (Acholuric jaundice ∵ haemolysis but NO tea colour urine ∵ unconjugated bilirubin (vs in obstructive jaundice))
3. ***Haemoglobinuria in intravascular haemolysis (e.g. Paroxysmal nocturnal haemoglobinuria (PNH), massive haemolysis due to drug-induced haemolysis in G6PD deficiency)
4. ***Splenomegaly
   - Acute hemolytic anemias cause splenomegaly with congestion (bloody spleen) (web)
   - Chronic: decreased sequestration of diseased erythrocytes —> less congestion but is instead attributed to diffuse proliferation of macrophages, phagocytosis, and concurrent hyperplasia of the white pulp due to ongoing antigenic stimulation

Question 6

***Laboratory features of Haemolytic anaemia

Answer 6

1. CBP
   - Anaemia (mildly **macrocytic usually)
   - **Reticulocytosis
2. Biochemistry
   - **↑ Unconjugated bilirubin, ↑ LDH
   - **↓ serum Haptoglobin (Hb bind to serum Haptoglobin —> use up Haptoglobin first)
   - ***↑ Methaemalbumin (Hb then bind to Albumin —> ↑ Methaemalbumin)
3. Blood film
   - ***Polychromasia (∵ reticulocytosis)
   - Spherocytes (in Hereditary spherocytosis, Immune haemolytic anaemia)
   - RBC fragmentation (Schistocytes) (in MAHA)
   - RBC agglutination (in Cold agglutinin disease)
4. Other investigation
   - ***Direct antiglobulin test (DAT) / Direct Coombs test —> positive in Immune haemolytic anaemia

Question 7

Autoimmune Haemolytic Anaemia (AIHA)

Answer 7

• Autoimmune Ab against self RBC
• Warm / Cold AutoAb (depending on temp which Ab binds better to RBC)

Warm type (37oC)
- **IgG
Causes:
1. Idiopathic
2. Secondary
- Drugs e.g. **Methyldopa
- Autoimmune diseases e.g. **SLE
- Lymphoproliferative disorders e.g. **CLL, Follicular lymphoma

Cold type (4oC)
- IgM
Causes:
1. Idiopathic (Cold agglutinin disease —> **Acrocyanosis)
2. Secondary
- Infections e.g. **Mycoplasma pneumonia, ***Infectious mononucleosis
- Lymphoproliferative disorders

Question 8

Diagnosis of AIHA

Answer 8

1. CBP
   - ↓ Hb
   - ***↑ Reticulocyte
2. Blood film
   - ***Polychromasia
   - Microspherocytes
3. Biochemistry
   - ↑ Unconjugated bilirubin, ↑ LDH
   - ↓ Haptoglobin
   - ↑ Methaemalbumin
4. Specific tests
   - ***Direct antiglobulin test (DAT): test for presence of AutoAb coating RBC in patient
   —> add Antihuman Ab (Coombs agent, from animals)
   —> Antihuman Ab binds to AutoAb on RBC
   —> form links between RBC
   —> RBC agglutinate
   (DAT can also test for AlloAb)

Question 9

Treatment of AIHA

Answer 9

1. Transfusion if necessary
2. **Folate supplement (for **all patients with ***any form of haemolytic anaemia, ∵ ↑ in demand for folate)
3. Decrease further haemolysis
   - **Steroids / immunosuppressants in AIHA
   - Avoidance of certain drugs in drug-induced haemolytic anaemia
   - **Keep warm in cold agglutinin disease
   - ***Splenectomy
4. Treat underlying cause if necessary
   - e.g. AIHA due to underlying Lymphoproliferative disorder, SLE

Question 10

Aplastic anaemia

Answer 10

• Pancytopenia resulting from ***BM hypoplasia / aplasia / failure

Classification:
- Congenital
- Acquired (Idiopathic vs Secondary to some BM insult)

• Isolated aplasia of Erythroid series: **Pure red cell aplasia (PRA)
  —> Congenital: **Diamond-Blackfan syndrome
  —> Acquired: ***Lymphoproliferative disease, Thymoma, Parvovirus B19

Etiology:
1. **Idiopathic (70-80%) (believed to be **Autoimmune)

2. Congenital (rare)
   - Fanconi anaemia, Dyskeratosis congenita, Shwachman-Diamond syndrome
3. Drugs (cause aplasia / suppression of BM)
   - **Gold, Alcohol, Diclofenac acid, **Indomethacin, Chloramphenicol, ***Anticonvulsants
4. Infection
   - ***Non-A, B, C hepatitis (sero-negative hepatitis)
5. Environmental exposure
   - Benzene, Pesticide

Question 11

Pathogenesis of Idiopathic Aplastic anaemia

Answer 11

Can be considered an Autoimmune disease:
- Immune (***T-cell) mediated suppression of BM stem cells

Question 12

Clinical features of Aplastic anaemia

Answer 12

1. ***Pancytopenia symptoms
   - Anaemia
   - Neutropenia (infection risk)
   - Thrombocytopenia (bleeding tendency)
2. ***NO lymphadenopathy
3. ***NO hepatosplenomegaly
4. In young patients, watch out for presence of **congenital physical abnormalities (indicate **Inherited BM failure syndromes)
   - e.g. Fanconi anaemia, Dyskeratosis congenita, Shwachman-Diamond syndrome

Question 13

Investigations of Aplastic anaemia

Answer 13

1. CBP
   - Pancytopenia
   - Macrocytic anaemia
   - ***Low reticulocyte count
2. Blood film
   - No Polychromasia
   - No Abnormal cells
3. ***Autoimmune markers
   - see if autoimmune process e.g. SLE
4. ***B12, Folate level
   - see if B12, Folate deficiency
5. **BM trephine biopsy
   - required for assessment of **cellularity
   - aspiration cytology not good enough
6. Specialised test
   - Flow cytometry for CD55, CD59 deficient RBC (to rule out PNH ∵ PNH also associated with Aplastic anaemia)
   - Chromosome breakage with diepoxybutane (to screen for ***Fanconi anaemia (Inherited BM failure syndromes))

Question 14

Definition of Severity of Aplastic anaemia

Answer 14

1. Severe aplastic anaemia
   - BM cellularity ***<25%
   2 of 3 of following cytopenia:
   - Neutrophil <0.5
   - Platelet <20
   - Reticulocyte <20
2. Very severe aplastic anaemia
   - same as above but Neutrophil <0.2

Question 15

Treatment of Aplastic anaemia

Answer 15

Mild / Moderate:
- NO treatment
- Support with ***blood products

Severe:
1. 1st line: **Allogeneic HSCT (for **young patients with matched sibling donors)
2. Anti-thymocyte/lymphocyte globulin (ATG) + **Cyclosporine
3. Cyclosporine A only
4. Support with blood products, Fe chelation
5. **Eltrombopag (thrombopoietin receptor agonist, high dose) + **ATG + **Cyclosporine —> very high response rate —> now standard for those cannot undergo AlloHSCT

Question 16

***Inherited BM failure syndromes

Answer 16

Pancytopenia:
1. Fanconi anaemia
2. Dyskeratosis congenita
3. Shwachman-Diamond syndrome

Anaemia (Isolated aplasia of Erythroid series: ***Pure red cell aplasia (PRA)):
1. Diamond-Blackfan anaemia
2. Congenital dyserythropoietic anaemia

Question 17

Fanconi anaemia, Dyskeratosis congenita, Shwachman-Diamond syndrome, Diamond-Blackfan syndrome, Congenital dyserythropoietic anaemia

Answer 17

X rmb

1. Fanconi anaemia
   - Inheritance: AR, XLR
   - **Somatic abnormalities: Yes (missing thumb, hyper / hypopigmentation of skin)
   - **BM failure: Aplastic anaemia
   - Short telomeres: Yes
   - ***Malignancy (perhaps ∵ chromosomal instability): Yes
   - Chromosome instability: Yes
   - Genes involved: 13
2. Dyskeratosis congenita
   - Inheritance: XLR, AR, AD
   - Somatic abnormalities: Yes (reticulosis in skin, nail dystrophy, leukoplakia)
   - BM failure: Aplastic anaemia
   - Short telomeres: Yes
   - Malignancy: Yes
   - Chromosome instability: Yes
   - Genes involved: 6
3. Shwachman-Diamond syndrome
   - Inheritance: AR
   - Somatic abnormalities: Yes
   - BM failure: Aplastic anaemia
   - Short telomeres: Yes
   - Malignancy: Yes
   - Chromosome instability: Yes
   - Genes involved: 1
4. Diamond-Blackfan syndrome
   - Inheritance: AD
   - Somatic abnormalities: Yes
   - BM failure: Pure red cell aplasia
   - Short telomeres: ?
   - Malignancy: Yes
   - Chromosome instability: ?
   - Genes involved: 7
5. Congenital dyserythropoietic anaemia
   - Inheritance: AR, AD
   - Somatic abnormalities: Rare
   - BM failure: Ineffective erythropoiesis
   - Short telomeres: ?
   - Malignancy: No?
   - Chromosome instability: ?
   - Genes involved: 1

Question 18

Inherited causes of anaemia: Pathophysiology

Answer 18

1. Inherited BM failure syndromes: Pancytopenia, Pure red cell aplasia (PRA)
2. Membranopathy —> Haemolytic anaemia
3. Haemoglobinopathy (Thalassaemia) —> Haemolytic anaemia
4. RBC metabolism disorders (Enzymopathy) —> Haemolytic anaemia

Question 19

History taking in Inherited causes of Anaemia

Answer 19

1. Family history
   - ***pattern of inheritance
2. ***Age of onset
   - tend to present at early age
3. Drug history
   - G6PD deficiency: only develop haemolysis when challenged by ***oxidising drugs
4. Symptoms of haemolysis
   - ***Jaundice
5. ***Transfusion requirement
   - long term transfusion in Hereditary spherocytosis
6. Complications
   - including those due to long-term red cell transfusion e.g. ***Fe overload

Question 20

***Clinical features in Inherited causes of Anaemia

Answer 20

1. Pallor
2. Jaundice
3. Splenomegaly
4. ***Skin complexion
5. ***Skeletal deformities

Question 21

Disorders of RBC membrane (Membranopathy)

Answer 21

Types:
1. Hereditary spherocytosis (loss of central pallor)
2. Hereditary elliptocytosis + Hereditary pyropoikilocytosis
3. Southeast Asian ovalocytosis
4. Hereditary acanthocytosis (not necessarily inherited, could be associated with liver disease)
5. Hereditary stomatocytosis

Pathophysiology:
- Mutation in genes encoding ***cytoskeleton protein (responsible for vertical / horizontal interaction)

X rmb
1. α-spectrin
- cytoskeleton network
- Hereditary spherocytosis (HS), Hereditary elliptocytosis (HE)

2. β-spectrin
   - cytoskeleton network
   - Hereditary pyropoikilocytosis, HS, HE
3. Ankyrin
   - vertical contact
   - HS
4. Band 3
   - anion exchange channel
   - HS, SEA ovalocytosis, Hereditary acanthocytosis
5. Protein 4.1
   - spectrin-actin contact
   - HE
6. Protein 4.2
   - spectrin-ankyrin interaction
   - HS (Japan)

Question 22

Hereditary spherocytosis

Answer 22

• Spherocytes on blood film (only 20% of all RBC (SpC Paed))
• Haemolytic anaemia: mild (well compensated) - severe
• ***Extravascular haemolysis —> No Haemoglobinuria
• AD
• 60% result from defect in ***Ankyrin-Spectrin complex / Vertical interaction

Clinical feature:
1. **Jaundice (Unconjugated hyperbilirubinaemia)
2. **Splenomegaly
3. **Gallstone
4. **Aplastic crisis (Primary ***parvovirus B19 infection during chronic haemolysis)

CBP:
1. Spherocytes on blood film
2. Extravascular haemolysis
3. ***MCHC often ↑ (∵ cellular dehydration)

Investigations:
1. Osmotic fragility test (past) (∵ spherocytes more susceptible to osmotic lysis)
2. Flow cytometry: ***Eosin-5-maleimide binding (↓ binding of RBC to the dye in HS)

Question 23

Treatment of Hereditary spherocytosis

Answer 23

1. ***Folate supplement (as in all haemolytic anaemia)
2. Compensated haemolysis: No specific treatment (no / mild anaemia)
3. ***Cholecystectomy (if symptomatic gallstones)
4. Splenectomy (if severe haemolysis)

Question 24

Disorders of Haemoglobin

Answer 24

1. Thalassaemia
   - Hb disorders with ***↓ in rate of synthesis of >=1 globin chains
2. Haemoglobinopathies
   - Hb disorders with a ***structurally abnormal Hb e.g. HbS
   - in some cases, there are concomitant ↓ synthesis of globin chains (i.e. “Thalassaemic haemoglobinopathies” e.g. Hb Constant Spring, HbE)

Question 25

Disorders of RBC metabolism (Enzymopathy)

Answer 25

aka **Congenital non-spherocytic haemolytic anaemia (∵ no spherocytes vs Hereditary spherocytosis / Immune-mediated haemolysis)
1. **G6PD deficiency
2. ***Pyruvate kinase deficiency
3. Deficiency of other glycolytic pathway enzymes (rare)

G6PD deficiency:
- important in generation of reducing power: GSH
—> needed to withstand oxidative stress (esp. RBC always in contact with O2)

Glycolytic enzyme deficiency:
- RBC nucleus expelled in BM before in circulation
—> no protein synthesis
—> rely on existing enzymes to generate energy to maintain protein integrity / osmolality
—> deficiency in enzymes
—> no ATP generated
—> RBC susceptible to haemolysis

Question 26

G6PD deficiency

Answer 26

• ***X-linked recessive
• Incidence in HK: 4.5% in males, 0.5% in females
• > 100 variants associated with enzyme deficiency
• Type B refers to Wild-type

Classified based on severity (residual enzyme activity):
Class 1: Severe <2%, Santiago de Cuba (Gly447Arg) —> Haemolytic anaemia (unprovoked chronic haemolysis), acute exacerbation
Class 2: **<10%, Canton (Arg45Leu), Mediterranean (Ser188Phe) —> Favism, Acute IV haemolysis (drug induced), Neonatal Jaundice
Class 3: Moderate **<60%, A- (Val68Met, Asn126Asp) —> No clinical effect
Class 4: ***100%, Type B (wild type), Type A (Asn126Asp) —> No clinical effect

Clinical features:
1. Intravascular Haemolysis with Haemoglobinuria (acute / chronic) (not common)
2. Precipitated by infection, acute medical illness, drugs, fava beans (most of the time)
- drugs: Sulphonamides, Rasburicase, Primaquine

Investigation:
1. Blood film
- Polychromasia
- ***Ghost / Hemi-ghost cells (∵ oxidative changes)
—> ghost: no Hb in cell (can only see membrane) (得返個殼)

Diagnosis:
1. **G6PD assay for enzyme level
- may be **normal during acute phase (i.e. acute haemolysis) as young RBC and reticulocytes may have normal G6PD levels

Treatment:
1. Supportive
2. **Blood transfusion
3. **Folate supplement
4. Stop + Avoid offending agents

Question 27

Revision: Haemolytic anaemia

Answer 27

Destruction of RBC accelerated —> shortened RBC life span
- may not have anaemia in presence of adequate marrow compensation
—> compensated haemolysis

Extravascular haemolysis: Spleen: Macrophage clearing up damaged/defective RBC, Warm AIHA
Intravascular haemolysis: G6PD deficiency, Microangiopathic haemolytic anaemia, Cold AIHA

Causes:
- Intrinsic / Extrinsic (See previous note)
- Acquired / Inherited

Acquired
1. Immune-mediated
- Ab to RBC surface antigens
—> Spherocytes + ***positive DAT

2. Microangiopathic
   - mechanical disruption of RBC in circulation
   —> Red cell fragmentation syndromes
   —> Schistocytes
3. Infection
   - Malaria, Clostridium
   —> cultures, serologies

Hereditary
1. Enzymopathies
- G6PD deficiency
—> Low G6PD activity

2. Membranopathies
   - Hereditary spherocytosis
   —> Spherocytes, family history, ***negative DAT (vs Warm AIHA)
3. Hemoglobinopathies
   - Thalassaemia, Sickle cell disease
   —> Hemoglobin electrophoresis, genetic studies

Laboratory findings:
1. Increased Haemoglobin breakdown (↑ Total + Unconjugated Bilirubin)

2. Red cell damage
   - **Spherocytes (Hereditary spherocytosis / Warm AIHA)
   - **Schistocytes (Microangiopathic haemolytic anaemia)
   - Sickle cell (Sickle cell anaemia)
3. Reticulocytosis (Polychromasia)
4. Circulating nucleated RBC
5. Erythroid hyperplasia (in BM)
6. Intravascular haemolysis
   RBC damaged in circulation
   —> release free Hb (↑ plasma Hb)
   —> Free Hb bind to Haptoglobin first (↓ Haptoglobin)
   —> Haptoglobin used up
   —> Hb bind to Albumin (↑ Methaemalbumin, +ve Schumm’s test)
   —> Excess Hb:
7. Haemoglobinaemia
8. Filter in glomerulus (Haemoglobinuria —> Dark urine)
9. Iron deposition in renal tubules (Haemosiderin) —> re-excreted in urine inside dislodged cells (Haemosiderinuria: Sign of chronic intravascular haemolysis)

Question 28

Revision: Autoimmune haemolytic anaemia

Answer 28

RBC destruction mediated by Ab directed against RBC antigens
- Spherocytosis (warm AIHA)
- RBC agglutination (cold AIHA)

1. Autoimmune (AutoAb)
   - warm / cold
   - many idiopathic
   - associated with autoimmune disease (e.g. SLE), lymphoproliferative disorder, mycoplasma pneumonia, infectious mononucleosis
   - +ve DAT
2. Alloimmune (AlloAb)
   - Haemolytic transfusion disorder (ABO incompatible blood transfusion)
   - Haemolytic disease of newborn (Anti-D in Rh D -ve mother —> haemolysis in Rh D +ve infant)
3. Drug-induced
   - Hapten mechanism: Ab directed against drug-cell membrane complex
   - Immune complex mechanism: drug-Ab complex on RBC surface —> Complement deposition
   - Autoimmune

Question 29

Revision: Thalassemia

Answer 29

Hyperproliferative anaemia

Genetic disorder of globin chain synthesis
- ↓ synthesis of particular globin chains
—> imbalance in available globin chains
—> excess chains polymerise but **unstable
—> precipitate
—> **Early destruction of RBC precursors in BM (ineffective erythropoiesis) / ***Shorten RBC life span

Laboratory findings:
- ***Hypochromic Microcytic RBC (defective haemoglobinisation)
- Abnormal globin tetramers (Hb H / Hb Barts) / Normal haemoglobin present in non-physiological amount (e.g. Hb F)
—> Increased O2 affinity
—> Tissue hypoxia (cannot unload O2)

**Laboratory diagnosis of Thalassaemia:
1. CBC, RBC indices
2. Peripheral blood film
- **Hypochromic, Microcytic
- **Reticulocytosis
- Anisocytosis (嚴重先有)
- Poikilocytosis (嚴重先有)
- Normoblasts
- **Target cells
3. β-Thalassaemia —> **Hb F, Hb A2 quantitation by chromatography / electrophoresis
4. α-Thalassaemia —> Detection of **Hb H inclusions
5. Genotyping for complex cases / Prenatal diagnosis

Prevention of Hb Bart’s hydrops fetalis and β-Thalassemia Major
1. Public health education
2. Counselling of specific target groups (couples before / soon after marriage)
3. Carrier detection
4. Antenatal, Prenatal diagnosis

Question 30

Revision: α-Thalassaemia

Answer 30

• defective fetal + adult Hb production
• Fetus: excess γ chains (Hb Bart’s: γ4)
• Adult: excess β chains (Hb H: β4)
  —> may be masked during smear examination by concomitant β-Thalassemia
  —> ∵ cannot produce β-chains

1. α-Thalassaemia trait (1 / 2 gene deletion)
   - 1 gene deletion: clinically / haematological silent
   - 2 gene deletion: normal / slightly ↓ haemoglobin, **↑ RBC count, **Hypochromic Microcytic RBC
   - ***HbH inclusions: precipitated out to form blue-green granules when RBC incubated with Brilliant cresyl blue stain (哥爾夫球)
2. Hb H disease (3 gene deletion)
   - **Chronic anaemia
   - **Splenomegaly (to remove RBC)
   - ***~ALL patient have normal physical development (small proportion has thalassaemic facies)
   - can be Asymptomatic
   - generally NOT transfusion dependent
   - excess β chains —> Hb H (5-40% total Hb)
   - small amount of Hb Bart may be present
   - variable features
   - exacerbated by pregnancy / infection
   - Complication: Hypersplenism —> Splenectomy indicated
3. Hb Bart’s hydrops fetalis (4 gene deletion)
   - no α-chain found
   - incompatible with life (unless start vigorous treatment early in fetal life)
   - excess γ chains —> Hb Bart’s (γ4)
   - edematous fetus due to **heart failure (a result of anaemia) and **liver dysfunction
   —> condition diagnosed with ultrasonography, confirmed with prenatal genetic diagnosis

Molecular genetics
- 90% due to deletions of DNA (vast majority removal of both α-genes from α-gene cluster, single α-gene deletions less common)
- 10% due to **non-deletional type (*Hb Constant Spring, Hb Quong Sze) —> more severe S/S, complications

Question 31

Revision: β-Thalassaemia

Answer 31

Reduced (β+) / Absent (βo) synthesis of β-globin chain

• β chain production only becomes predominant in post-natal period
  —> severe β-Thalassemia (β-Thalassemia major) manifest only when patient >= 3 months old (大個d先見到Symptoms)

1. β-Thalassemia Trait / Minor
   - **Heterozygous for βo / β+
   - Asymptomatic
   - slightly ↓ Hb level
   - **↓ MCV (Microcytic), ↓ MCH (Hypochromic)
   - **↑ RBC count
   - **↑ Hb A2 (MOST important diagnostic feature for heterozygous β-Thalassemia)
   - many have minor ↑ Hb F
2. β-Thalassemia Major (Cooley’s anaemia)
   - total absence / marked reduction of β-globin chains
   —> excessive α-globin chains precipitate out in RBC precursor cells
   —> extensive intramedullary destruction of RBC precursors (**Ineffective erythropoiesis)
   —> **marked expansion of BM —> Hyperproliferative anaemia
   - **↑ destruction of peripheral RBC (Haemolytic element)
   - **↑ Hb F level —> ***selective survival advantage (explain high level of Hb F)

Blood film:
- Marked RBC Anisocytosis (↑ RDW) + **Poikilocytosis
- **Hypochromic
- ***Numerous nucleated RBC (Normoblast)

Homozygous βo:
- complete absence of Hb A
- small amount of Hb A2
- ***HbF remainder (98%)

Clinical features:
1. Thalassaemic facies
2. Protuberant abdomen (Hepatosplenomegaly)
3. ***Poor musculoskeletal development
4. Complications e.g. Recurrent infections, spontaneous fractures, hypersplenism, leg ulcers, extramedullary haemopoiesis

Treatment:
- **Blood transfusion
- **Iron overload —> Treat with ***Iron chelation therapy (Deferoxamine)

***3 Major genetic modifiers of disease severity (can be modified to milder clinical severity e.g. Thalassemia Intermedia):
—> Nature of β-globin gene defect (whether mutation associated with severe phenotype)
—> Configuration of α-globin gene locus (affect degree of α/β globin gene imbalance)
—> Genetic determinants of Hb F level

3. Thalassemia Intermedia (Non-transfusion dependent Thalassemia (NTDT))
   - symptomatic but milder than β-Thalassemia Major
   —> β-Thalassemia Intermedia
   —> Hb H disease
   —> Hb E β Thalassemia

Hb E:
- Haemoglobinopathy
- point mutation of β gene at position 26 —> a.a. change from Glutamate to Lysine —> Abnormal Hb (Hb E)
- mRNA of Hb E —> unstable —> **underproduced abnormal Hb —> thalassaemic presentation
- Heterozygous HbE —> Mild Microcytosis, No/Minimal anaemia (some have totally normal CBP)
- Homozygous HbE —> Microcytosis, Mild anaemia
- Compound heterozygous HbE + β-Thalassaemia —> Thalassaemia Intermedia syndrome, **Splenomegaly, other complications

Molecular genetics of β-Thalassaemia
- Point mutations (NOT gene deletions)
- Own unique set of mutations among different races