Thalassaemia is caused by faulty genes that a child inherits from their parents.

It's not caused by anything the parents did before or during the pregnancy, and you cannot catch it from someone who has it.

Genes come in pairs. You inherit 1 set from your mother and 1 set from your father.

To be born with the main type of thalassaemia, beta thalassaemia, a child has to inherit a copy of the faulty beta thalassaemia gene from both of their parents.

This usually happens when both parents are "carriers" of the faulty gene, also known as having the "thalassaemia trait".

Thalassaemia carriers do not have thalassaemia themselves, but there's a chance they could have a child with thalassaemia if their partner is also a carrier.

If both parents have the beta thalassaemia trait, there's a:

• 1 in 4 chance each child they have will not inherit any faulty genes and will not have thalassaemia or be able to pass it on
• 1 in 2 chance each child they have will just inherit a copy of the faulty gene from 1 parent and be a carrier
• 1 in 4 chance each child they have will inherit copies of the faulty gene from both parents and will be born with thalassaemia

Another type of thalassaemia, alpha thalassaemia, has a more complex inheritance pattern because it involves 4 potentially faulty genes, rather than just 2.

Children of parents who are carriers of the alpha thalassaemia trait will be born with the condition if they inherit 3 or 4 copies of the faulty gene.

Children who inherit 1 or 2 copies will be carriers.

Thalassaemia mainly affects people who are from, or who have family members originally from:

• around the Mediterranean, including Italy, Greece and Cyprus
• India, Pakistan and Bangladesh
• the Middle East
• China and southeast Asia

A simple blood test will show whether you're a carrier. This is done routinely during pregnancy and after birth, but you can ask to have the test at any time.

Read more about getting tested for the thalassaemia trait and being a carrier of thalassaemia.