What is sickle cell disease?
What is the definition of sickle cell disease?
Sickle cell disease or falciform anaemia is an inherited condition caused by a genetic mutation that leads to the production of abnormal haemoglobin in red blood cells.
The role of haemoglobin is to transport oxygen to all the organs. It is the main component of red blood cells. Normally round and flexible, the red blood cells of a person with sickle cell disease become deformed and take on the shape of sickles – rigid and curved – hence the name of the disease (Drepanon means sickle in Greek) and in English, ‘sickle cell disease’ means ‘disease of the sickle-shaped cells’.
In certain situations, for example when a person with sickle cell disease is dehydrated, lacks oxygen or is cold, this phenomenon becomes more pronounced and triggers painful crises.
In people with sickle cell disease the deformation of red blood cells limits the cells’ ability to carry oxygen and to circulate, particularly in small blood vessels, and can even block them, causing pain, fatigue, anaemia, an increased risk of infection and organ damage.
Normal red blood cells |
Abnormal red blood cells |
Every year, around 500,000 babies are born with sickle cell disease, 80% of them in sub-Saharan Africa. In some countries, these patients may account for 1 to 2% of births. These figures highlight the crucial importance of programmes for the prevention, information about and management of the disease in order to reduce its burden.
Learn more: How is sickle cell disease spread and diagnosed?
What causes sickle cell disease?
Sickle cell disease is an inherited condition caused by a genetic mutation.
The haemoglobin found in a healthy person is haemoglobin A (Hb A). The most common mutation in people with sickle cell disease leads to the production of haemoglobin S (HbS).
For an individual to have sickle cell disease, they must inherit two haemoglobin S genes (Hb SS), one from the father and one from the mother. If the individual inherits only one haemoglobin S gene, they will then be known as having the HbAS1 form of the disease and will be a healthy carrier without being ill themselves, but they may pass on the HbS gene to their offspring children. In this case, they are said to be a carrier of the sickle cell trait.
Another mutation in the haemoglobin gene can also cause sickle cell disease; this is the C mutation. Patients who carry haemoglobin C (Hb SC or Hb CC) also have sickle cell disease, but their symptoms differ in some respects from those of HbSS patients.
In sub-Saharan Africa, around 15% of the population carries the sickle cell trait.
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[1] Be consistent with the use of Hb pour haemoglobin and the type of mutation: eg. HbSS or Hb SS; with a space or no space in between the two.
Learn more: What is the risk of having a child with sickle cell disease? And what should be done if there is a risk?
What are the different types of sickle cell disease?
There are different types of sickle cell disease depending on the genetic abnormality in the patient’s haemoglobin. For example, patients living with what is known as‘SS’ sickle cell disease have inherited two haemoglobin S genes. They generally have a reduced red blood cell count, painful episodes and damage to various organs.
Patients living with what is known as ‘SC’ sickle cell disease have inherited one haemoglobin S gene and one haemoglobin C gene. ‘CC’ patients have inherited two haemoglobin C genes. Patients living with sickle cell anaemia known as ‘SC’ or ‘CC’ generally have a normal or even increased red blood cell count, painful episodes and premature bone changes, most commonly in the hips.
Know more: Why are certain populations more affected?
Références ___________________________________________________________
Organisation Mondiale de la Santé. (2020). Drépanocytose.
National Heart, Lung, and Blood Institute. (2022). What Is Sickle Cell Disease?
Centers for Disease Control and Prevention. (2021). Sickle Cell Disease.