What Is Thalassaemia
Thalassaemia is an inherited impairment of hemoglobin production, in which there is partial or complete failure to synthesise a specific type of globin chain. In alphathalassaemia, disruption of one or both alleles on chromosome 16 may occur, with production of some or no alpha globin chains. In beta-thalassaemia, defective production usually results from disabling point mutations causing no (β0) or reduced (β–) beta chain production.
Types of thalassaemia:
Failure to synthesise beta chains (beta-thalassaemia) is the most common type of thalassaemia, most prevalent in the Mediterranean area. Heterozygotes have thalassaemia minor, a condition in which there is usually mildanaemia and little or no clinical disability, which may be detected only when iron therapy for a mild microcytic anaemia fails. Homozygotes (thalassaemia major) either are unable to synthesise haemoglobin A or, at best, produce very little; after the first 4–6 months of life, they develop profound hypochromic anaemia. The diagnostic features are summarised in Intermediate grades of severity occur.
Reduced or absent alpha chain synthesis is common in Southeast Asia. There are two alpha gene loci on chromosome 16 and therefore each individual carries four alpha gene alleles.
- If one is deleted, there is no clinical effect.
- If two are deleted, there may be a mild hypochromic anaemia.
- If three are deleted, the patient has haemoglobin H disease.
- If all four are deleted, the baby is stillborn (hydrops fetalis). Haemoglobin H is a beta-chain tetramer, formed from the excess of beta chains, which is functionally useless, so that patients rely on their low levels of HbA for oxygen transport. Treatment of haemoglobin H.
Diagnostic features of beta-thalassaemia
Beta-thalassaemia major (homozygotes)
- Profound hypochromic anaemia
- Evidence of severe red cell dysplasia
- Absence or gross reduction of the amount of haemoglobin A
- Raised levels of haemoglobin F
- Evidence that both parents have thalassaemia minor
Beta-thalassaemia minor (heterozygotes)
- Mild anaemia
- Microcytic hypochromic erythrocytes (not iron-deficient)
- Some target cells
- Punctate basophilia
- Raised haemoglobin A2 fraction
Treatment of beta-thalassaemia major
Erythropoietic failure Allogeneic HSCT from HLA-compatible sibling Transfusion to maintain
Hb > 100 g/L Folic acid 5 mg daily.
Iron overload Iron therapy contraindicated Iron chelation therapy.
Splenomegaly causing mechanical problems, excessive transfusion needs Splenectomy.