Thalassaemia - Causes of thalassaemia

It's not known exactly what causes the genetic mutations associated with thalassaemia.

It's likely the mutations have survived because carriers of the condition (both alpha and beta thalassaemia) are protected against malaria.

This is why thalassaemia and other related genetic blood disorders, such as sickle cell anaemia, are more common in parts of the world where malaria is a problem, such as:

• countries in the Mediterranean basin, such as Greece, Cyprus and Italy
• the Middle East
• Asia
• sub-Saharan Africa

How beta thalassaemia is inherited

Every person receives two sets of genes, one from their father and one from their mother. If a person receives one set of mutated genes, they're said to have the thalassaemia trait.

If that person has a baby with someone who also has the thalassaemia trait, there's a significant chance that the baby will receive two sets of mutated genes and develop thalassaemia.

The chances of the thalassaemia trait being passed on are described below.

• There's a one in four chance that the baby will receive a pair of normal haemoglobin genes.
• There's a one in two chance that the baby will receive one normal gene and one mutated gene. In this case, they won't have thalassaemia but they will have the thalassaemia trait.
• There's a one in four chance that the baby will receive a pair of mutated genes and have thalassaemia.

If one parent has the thalassaemia trait and the other parent has normal haemoglobin, their baby won't have thalassaemia. However, there's a one in two chance that the baby will receive the thalassaemia trait.

Beta thalassaemia affects the two genes that the body uses to produce the beta chain found in haemoglobin. Haemoglobin needs both an alpha and beta chain to work properly.

If only one gene is mutated, a person will have the beta thalassaemia trait. Most people won't have any symptoms, but some people may have mild anaemia.