Understanding
sickle cell disease

Sickle cell disease starts with genetics

When two parents have the trait, there’s a 50% chance that their child will have the trait, a 25% chance that the child will not have the trait, and a 25% chance the child will have sickle cell disease

Your body contains many sets of genes which you get from your birth parents. Each set plays a unique role in your body, such as determining your eye colour or skin tone. Another set of genes determines how red blood cells are made and how they work which is not a feature you can easily see. Those genes are called the haemoglobin [hee-muh-gloh-bin] genes, named after the protein in red blood cells that helps carry oxygen through your body.

You inherit one haemoglobin (Hb) gene from each parent. People who carry the sickle cell trait have one normal haemoglobin gene (HbA) and one sickle haemoglobin gene (HbS). HbS causes red blood cells to turn into a sickle shape. Having the sickle cell trait does not mean that someone has a “trace” sickle cell disease. It’s the opposite, actually. The sickle cell trait is completely separate from the disease; it may possibly cause symptoms, but instances of this are rare.

Depending on the set of haemoglobin genes you get from your parents, you will:

  • Have sickle cell disease

  • Carry the sickle cell trait, but not have sickle cell disease

  • Not have sickle cell disease and not carry the sickle
    cell trait

When two parents have the trait, there’s a 50% chance that their child will have the trait, a 25% chance that the child will not have the trait, and a 25% chance the child will have sickle cell disease

If you or a family member has been affected by sickle cell disease, then you may already be aware of this information. It is important to understand that the risk remains the same each time two sickle cell trait carriers have a child. If a couple’s first child has sickle cell disease, a second child has the same chance of being born with the disease. This means each child a couple has could potentially have sickle cell disease.

Your disease depends on the type of genes you have

Sickle cell disease actually refers to a group of different types of blood disorders caused by “sickle” haemoglobin (HbS). HbS is what all people with sickle cell disease have in common. However, there are different types of sickle cell disease. The specific type someone has depends on the kind of haemoglobin, beyond HbS, that you get from your birth parents.

Types of sickle cell disease include HbSS, HbSC, HbS- thalassemia, HbSD, HbSE, and HbS0
Types of sickle cell disease include HbSS, HbSC, HbS- thalassemia, HbSD, HbSE, and HbS0

When two birth parents have HbS, their child can have HbSS which happens to be the most common type of sickle cell disease worldwide.

Types of sickle cell disease include HbSS, HbSC, HbS- thalassemia, HbSD, HbSE, and HbS0

There are other possible changes to the haemoglobin gene which birth parents can also pass on to their children.

For example:

  • HbSC

  • HbS ß-thalassemia [thal-uh-see-mee-uh]

Like HbS, these genes limit how much oxygen red blood cells can carry through the body.

Any combination of HbS passed on with another haemoglobin gene, such as HbC and Hbß-thalassemia, can result in a child being born with sickle cell disease.

Sickle cell disease makes red blood cells less stable

The HbS gene causes red blood cells to become stiff and sickle shaped which affects the health of the cells. These unhealthy red blood cells break apart faster than healthy cells and it’s hard for the body to reproduce the blood cells it needs quickly enough. This creates a problem called anaemia which can make a person feel weak and tired.

Click on any of the blood cells below to learn more about their involvement in sickle cell disease

Normal red blood
Sickled red blood cells
Haemolysis
Anaemia
Normal red blood cells

The disc shape helps red blood cells squeeze through small blood vessels without being damaged. By keeping their healthy disc shape, red blood cells can carry oxygen through the body.

Sickle cell disease makes blood “sticky”

Sickle cell disease goes beyond red blood cells. The disease has an often silent, ongoing effect on blood vessels and other blood cells, too, such as white blood cells and platelets.

Click on any of the images below to learn more about what is happening inside the body, that leads to a pain crisis.

Blood cells stick to blood vessel walls and to each other

Stickiness

From an early age, sickle cell disease starts to damage and inflame the blood vessels. Damaged blood vessels become irritated and activate molecules in the blood called selectins [si-lekt-ins]. You can think of selectins as “sticky factors”. These sticky factors are what cause blood cells to stick to blood vessel walls and to each other.

Blood cells form clusters in the bloodstream

Clustering

As more and more blood cells interact with these "sticky factors", the cells get stuck to each other and to the vessel walls. This forms clusters in the bloodstream.

Your doctor may say multicellular adhesion
Blood flow is blocked

Blockages

The clusters build up and become blockages, making it difficult for blood and oxygen to flow normally. When you have sickle cell disease, the process of clusters forming and becoming blockages is ongoing.

Your doctor may say vaso-occlusion [vey-soh uh-kloo-zhun]

Understanding pain crises

Pain crisis in the body

When blood cell clusters get big enough, they can lead to a pain crisis. You may hear a doctor refer to pain crises as pain episodes or vaso-occlusive crises.

  • Vaso is a Latin term that refers to blood vessels. Occlusion is just another way of saying blockage.

The pain during a crisis can be severe and require medical attention. But often people with sickle cell disease suffer at home, without seeking medical help and support. Over time, these frequent pain crises can lead to long-term complications. That is why it is important to tell your health care provider about every pain crisis you or your child experience.

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