Thalassaemia

​What is thalassaemia?

Haemoglobin is the component in red cells that is responsible for transporting oxygen from the lungs to all parts of the body. Normal haemoglobin comprises two α globin chains and two β globin chains, and each of these protein chains carry an iron-containing haem group which binds to oxygen.

Haemoglobinopathies are a group of inheritable conditions which affect the quantity and/or structure of the haemoglobin. The most common haemoglobinopathy in Singapore and Southeast Asia is thalassaemia. 

In each individual, there are four α genes (two inherited from each parent) and two β genes (one inherited from each parent). They signal the production of the α globin chains and β globin chains respectively in haemoglobin. 

Persons with thalassaemia mutations of the α globin genes (α thalassaemia) have reduced production of α globin chains and those with thalassaemia mutations of the β globin genes (β thalassaemia) have reduced production of β globin chains, resulting in decreased quantities of haemoglobin.  

What are the different types of thalassaemia?

There are different types of thalassaemia, which are primarily classified into two main categories:

1. Alpha Thalassaemia: This type occurs when there is a mutation or deletion in one or more of the four genes responsible for making alpha-globin, a component of haemoglobin. The severity depends on how many genes are affected:

• Silent Carrier State: One gene is affected, usually no symptoms.
• Alpha Thalassaemia Trait: Two genes are affected, causing mild anaemia.
• Haemoglobin H Disease: Three genes are affected, leading to moderate to severe anaemia.
• Alpha Thalassaemia Major: All four genes are affected, resulting in a very severe condition that often causes stillbirth.
  

2. Beta Thalassaemia: This occurs when one or both of the genes responsible for producing beta-globin are mutated. It is categorised as:

• Beta Thalassaemia Minor (Trait): One gene is mutated, leading to mild anaemia.
• Beta Thalassaemia Intermedia: Both genes are mutated but the severity of anaemia is moderate.
• Beta Thalassaemia Major (Cooley's Anaemia): Both genes are severely mutated, causing severe anaemia that requires regular blood transfusions.