Sickle cell anaemia - Causes 

Causes of sickle cell anaemia 

A crescent- or sickle-shaped blood cell (left) alongside three normal shaped red blood cells 

Sickle cell anaemia is caused by a genetic mutation that affects the normal development of haemoglobin.

A genetic mutation is a permanent change in the normal pattern of genetic information inside all living cells. This results in one or more of the body's processes not working properly.

Haemoglobin

Haemoglobin is an iron-rich protein found in red blood cells. It enables the blood cells to carry oxygen from your lungs to the rest of your body.

As blood passes through your lungs, the haemoglobin pulls in oxygen and at the same time releases carbon dioxide. This process is known as oxygenation. 

After leaving your lungs, the haemoglobin delivers oxygen to the body’s tissue and removes excess carbon dioxide to take back to your lungs. This process is called deoxygenation.

During deoxygenation, healthy haemoglobin molecules smoothly rearrange themselves into a different shape. However, in sickle cell anaemia, the smooth rearrangement doesn't occur because of the mutated gene.

Instead, the haemoglobin inside blood cells clumps together into solid structures. The clumping distorts the normal shape of the red blood cells, causing them to take on a rigid, sickle shape.

The genetics of sickle cell anaemia

Genes come in pairs. You receive one copy of a gene from your mother and one copy from your father.

To have sickle cell anaemia, you would need to receive a pair of mutated genes – one mutated gene from your mother and one from your father.

If you only receive one mutated gene, you won't have sickle cell anaemia, but you'll be a carrier of the sickle cell gene. This is often referred to as having the sickle cell trait. It's estimated that one in 10 people of African or Caribbean descent has the sickle cell trait.

If you're a carrier, you won't usually notice any obvious symptoms unless you're somewhere where there's a low amount of oxygen in the air, such as on top of a mountain.

If both you and your partner have the sickle cell trait, there's a risk that any children you have will inherit a pair of mutated genes and develop sickle cell anaemia.

The chances of sickle cell anaemia being passed on are:

  • a one in four chance that your baby will receive a pair of normal haemoglobin genes
  • a one in two chance that your baby will receive one normal gene and one mutated gene and be a carrier of the sickle cell gene 
  • a one in four chance that your baby will receive a pair of mutated genes and have sickle cell anaemia

If one partner has the sickle cell trait and the other partner has normal haemoglobin, their baby won't develop sickle cell anaemia. However, there's a one in two chance that the baby will have the sickle cell trait.

If you have sickle cell anaemia and your partner has the sickle cell trait (or vice versa), any baby you conceive will have a one in two chance of developing sickle cell anaemia. This is because they'll definitely receive a mutated gene from you, and there's a one in two chance they'll also receive a mutated gene from your partner.

Read more about genetics.




Page last reviewed: 21/05/2014

Next review due: 21/05/2016

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Dr Nicky Thomas

Profile: Dr Nicky Thomas

As a consultant health psychologist, Dr Nicky Thomas supports people with sickle cell disorder to live as normal a life as possible.

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