Introduction

Thalassaemias are autosomal recessive inherited disorders of haemoglobin, causing structural deficiencies in haemoglobin molecules. As such, they are a type of haemoglobinopathy.

Haemoglobinopathies typically present with a microcytic hypochromic anaemia which will NOT respond to iron. In the most severe cases, thalassaemias can be fatal in utero or in the first few months of life, but most cases are of mixed genetic background and are mild.

Thalassaemia can be broadly classified into α-thalassaemia and β-thalassaemia, depending on the underlying structural haemoglobin changes. They are also often referred to as thalassaemia major, thalassaemia intermedia and thalassaemia minor – however this classification usually refers to the severity of the disease.

Haemoglobin molecules are made up of 4 “globin” chains. There are 4 type of globin chains; alpha (α), beta (β), gamma (γ) and delta (δ). Usually a haemoglobin molecule is made up of a pair of one type of globin chain (e.g. a pair of α chains) and then two other chains.

  • Most commonly, haemoglobin is made up of two alpha and 2 beta chains – HbA α22
  • Mutations in the alpha chains give rise to α-thalassaemia, and mutations in the beta chains give rise to β-thalassaemia

Over 300 mutations have been identified and the clinical severity of the disease varies widely.

  • Clinically, severe cases of thalassaemia manifest as haemolytic anaemia with splenomegaly (+/- hepatomegaly) and pallor (pale-looking) – often at birth or within the first few months of life.
  • Individuals with thalassaemia traits (either alpha or beta) are often asymptomatic
  • The clinically asymptomatic types of α-thalassaemia and β-thalassaemia produce a mild microcytosis – which often can appear like an iron-deficiency anaemia (but will often have normal iron studies). They will not respond to iron therapy

Epidemiology

  • 1.5% of the global population are carriers of β-thalaeeamia. Most prevalent in:
    • Mediterranean
    • Middle east
    • Southern China
    • Central, south and southeast Asia
  • 5% are carriers of α-thalassaemia. most prevalent in:
    • Southeast Asia
    • Africa
    • India

α thalassaemia

There are two genes that code for α chains. That’s easy to understand. And then thalassaemia starts to get very complicated.

There are 6 possible genotypes. You will definitely NOT be expected to know all of these unless you are a haematologist. But, for completeness – here they are*:

NameGenotypeInfo
Normal(a,a / a,a)No thalassaemia
α+ thalassaemia heterozygous(a,- / a,a)Clinically asymptomatic

↔ / ↓ Hb
↔ / ↓ MCV
↓ MCH
α+ thalassaemia homozygous(a,- / a,-)
Clinically asymptomatic
↓ Hb (slightly)
↓ MCV
↓ MCH
αo thalassaemia heterozygous(a,a / -,-)
Clinically asymptomatic
↓ Hb (slightly)
↓ MCV
↓ MCH
HbH disease(a,- / -,-)
Symptomatic
↓ Hb
↓↓ MCV
↓ ↓MCH
Splenomegaly
Bone changes
α thalassaemia major(-,- / -,-)
Usually fatal
↓↓ Hb (severe)
Severe intrauterine haemolytic anaemia

*I presume the genotype notation was first used before texting smiley faces became “a thing”!

  • Severe homozygous α thalassaemia is usually fatal in utero
    • Is one of the two main causes of hydros fettles – the other being rhesus incompatibility – which is now rarely seen.
  • α-thalasseamia carrier – refers to deletion of one α chain, and is asymptomatic
  • α-thalasseamia trait – refers to presentations with deletions of two α chains (a,- / a,-) or (a,a / -,- )
  • α-thalasseamia media – refer to HbH disease – whereby beta-haemoglobin chains replace this missing alpha-chains – and hence the predominance of HbH
    • HbH – haemoglobin H chains are an abnormal type of haemoglobin produced when a patient inherits an α+ from one parent and an αo from another
  • α-thalasseamia major – as above

β thalassaemia

There is only a single gene that codes for the beta chain – which makes β-thalassaemia slightly easier to understand!

NameGenotypeInfo
Normal22)No thalassaemia
β-thalassaemia trait( – / β2)
Clinically asymptomatic
↑HbA2 >4%
↓ Hb (slightly)
↓ MCV
↓ MCH
β-thalassaemia intermedia( – / β2) OR (β+/β+)
Symptomatic
↑HbF
↓ Hb (markedly)
↓↓ MCV
↓ ↓MCH
Splenomegaly
Bone changes
May require transfusion
β-thalassaemia major(-o / -o )
Symptomatic
↑HbF >90%
↓ Hb (markedly – severe haemolytic anaemia)
↓↓ MCV
↓ ↓MCH
Splenomegaly, hepatomegaly
Bone changes
Chronic transfusion dependency

Presentation

Defective β-chain synthesis usually results in increased alpha-chain synthesis. Excess alpha chains will precipitate in red cells and cause the red cells to be weakened. These fragile RBCs will subsequently be destroyed in bone marrow and the spleen. This causes a progressive splenomegaly as well as bone marrow proliferation – which results in bony deformities.

  • Homozygous disease usually presents by the age of 3 months, and if untreated can be fatal by the age of 1 year. Some may not present until as old as 5. Presenting features include:
    • Failure to thrive
    • Vomiting
    • Sleepiness
    • Irritability
    • Stunted growth
    • Fevers – due to hyper metabolic state
  • Most neonates with β-thalassaemia major are detected on blood spot screening at birth

Signs

In milder cases (Hb >90) there are rarely any signs or symptoms. In more severe case, signs can include:

  • Hepatoslpenomegaly
  • Bony deformities
    • Frontal bossing
    • Prominent facial bones
    • Dental deformities
  • Jaundice
  • Pallor
  • Cardiac flow murmur secondary to anaemia
  • Exercise intolerance

Differentials

Thalassaemia can be a differential for any other causes of a microcytic anaemia, such as:

  • Iron deficiency anaemia
  • Anaemia of chronic disease
  • Sideroblastic anaemia

Other differentials include:

  • Acute leukaemia
  • Rhesus incompatibility

Investigations

Blood

  • FBC
    • Microcytic hypochromic anaemia
    • May be confused with iron deficiency – especially β-thalassaemia
    • WCC may be elevated due to haemolysis
    • Platelets may be low due to splenomegaly
  • Iron studies
    • Increased ferritin
    • Saturation as high as 80%
  • Haemoglobin electrophoresis is diagnostic in β-thalassaemia
    • Checks for the presences of HbA2
      • Normal 1.5 – 3%
      • >3.5% is diagnostic for β-thalassaemia
  • DNA testing can be used to establish the underlying carrier status in families and parents

Imaging

  • X-ray may show bony changes
    • Skull – “hair on end” deformity
    • Maxilla – overbite and overgrowth
    • Long bones and ribs – may be flat or show other deformities
    • CXR – enlarged heart, signs of heart failure
  • CT / MRI
    • Can be used to assess the liver in patient on chelation therapy

Other potential investigations

  • ECG and Echo – to monitor cardiac function
  • Liver biopsy – to assess iron deposition and the degree of haemochromatosis
  • Bone marrow biopsy – may be needed to confirm diagnosis
  • HLA typing – in cases where bone marrow transplant is considered
  • Monitor of chelation therapy
    • Eye tests
    • Hearing tests
    • Renal function

Management

  • Blood transfusion prolongs survival but causes iron overload. Aim for Hb >95g/L. Consider using ‘leucocyte poor’ blood to prevention sensitisation – especially if future bone marrow transplant is an option
  • Indications for transfusion include:
    • Growth impairment
    • Skeletal deformity
  • Iron overload usually occurs as a result of multiple transfusions, but can occur without transfusion. Iron deposits widely in various organs in the body, causing fibrosis and organ failure. It can be treated with chelation
    • Patient still often suffer from restricted growth, and endocrine disorders secondary to iron overload, such as diabetes, thyroid disorders and adrenal and pituitary disorders
    • Be wary of ever giving iron supplementation to any thalassaemia patient – unless there is proven iron deficiency
  • Overall life-expectancy is reduced
  • Consider splenectomy if there is marked hypersplenism – be wary of risks of asplenism (life-threatening infections, VTE, pulmonary hypertension)
  • Bone marrow transplant is curative
    • Best outcome if done at earlier age
  • Offer genetic counselling to all patients with all variants of thalassaemia
  • Lifestyle factors:
    • Avoid foods rich in iron
    • Vitamins C+E, folic acid may be beneficial
    • Drinking tea and coffee frequently can reduce the absorption of iron

Prognosis

α thalassaemia

  • Excellent if only a carrier
  • HbH disease has variable prognosis. Most survive into adulthood, but some suffer many complications
  • Hydrops fettles is incomparable with life

β thalassaemia

  • Thalassaemia minor causes an asymptomatic microcytic anaemia with no effect on mortality or morbidity
  • Thalassaemia major carries an 80% mortality in the first 5 years of life
  • Patients who require transfusions have substantially reduced life expectancy
    • Without chelation – often will not survive teenage years
    • Chelation therapy has improve life-spans
  • Stem-cell transplant (bone marrow transplant) is associated with 85-90% survival after 15 years

References

  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.

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