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 can't catch it from someone who has it.
How thalassaemia is inherited
Genes come in pairs. You inherit one set from your mother and one 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 don't have thalassaemia themselves, but there's a chance they could have a child with the condition if their partner is also a carrier.
If both parents have the beta thalassaemia trait, there's a:
- 1 in 4 (25%) chance each child they have will not inherit any faulty genes and won't have thalassaemia or be able to pass it on
- 1 in 2 (50%) chance each child they have will just inherit a copy of the faulty gene from one parent and be a carrier
- 1 in 4 (25%) 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 four potentially faulty genes, rather than just two.
Children of parents who are carriers for alpha thalassaemia trait will be born with the condition if they inherit three or four copies of the faulty gene. Children who inherit one or two copies will be carriers.
Who's most at risk of thalassaemia?
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.
How thalassaemia affects the body
Your genes are the set of instructions found inside every cell in your body. They determine characteristics such as the colour of your eyes and hair.
People with thalassaemia have a problem with the genes involved in the production of haemoglobin – a substance found in red blood cells that's used to carry oxygen around the body.
In people with thalassaemia major or other severe types, either no or very little haemoglobin is produced, which can make them very anaemic if they don't have regular blood transfusions.