Sickel Cell Disease

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What is sickle cell disease (SCD)? – This is a group of inherited disorders in which red blood cells are produced with abnormal haemoglobin (the protein that transports oxygen in red blood cells). Red blood cells are oval-shaped and normally flexible. This helps them to alter their shape when passing through small blood vessels and organs like spleen, where they are screened to remove old and worn out red cells.  

In those with sickle cell disease, the abnormal haemoglobin in their red blood cells makes the red blood cells hard and to assume distorted shape, resembling a farm tool known as ‘sickle’. This makes it vulnerable to easy destruction by the spleen.

What is the problem of red cells in SCD?

In patients with sickle cell disease, the red blood cells die early because of their rigidity. While normal red blood cells have an average lifespan of 120 days, the red blood cells in sickle cell disease live an average of 10 to 20 days. This creates constant shortage of red blood cells (anaemia).

The sickle red cells also get stuck into small blood vessels and prevent free flow of blood due to their non-flexibility as a result of the abnormal haemoglobin. This is one of the ways they cause the problems associated with this condition such as generalised body pain, stroke, acute chest syndrome (severe chest pain that limits breathing), infection (due to shortage of blood supply) etc.

What are the types of sickle cell disease? 

As sickle cell disease is an inherited problem, the type of SCD someone has depends on the genes inherited from the parents. The common types of sickle cell disease are as follows:

  1. HbAS / HbAC (Sickle Cell Trait) – This occurs by inheriting abnormal (‘S’ or “C”) haemoglobin gene from one parent and normal (‘A’) haemoglobin gene from the other parent. The people in this category are otherwise normal, as they do not usually manifest any symptom of SCD. However, in extreme stressful conditions, they may manifest some mild symptoms of SCD.
  2. HbSC – This results from inheritance of an abnormal haemoglobin ‘S’ gene from one parent and another abnormal haemoglobin ‘C’ from the other parent. The resultant red blood cells have abnormal shape and are rigid; thereby easily destroyed by the spleen. However, the disease is milder in manifestation than HbSS.
  3. HbSS – This results from inheritance of two (abnormal) haemoglobin ‘S’ genes, one from each parent. This makes red cell to have abnormal (sickle) shape and be too rigid to pass through small blood vessels. They therefore prevent free flow of blood and are easily destroyed, leading to the affected person having insufficient red blood cells (anaemia). This is therefore referred to as sickle cell anaemia.
  4. HbS beta thalassemia – In this case, haemoglobin S gene, inherited from one parent, combines with another haemoglobin gene from the other parent that has inadequate beta-globin chain for haemoglobin A (haemoglobin has two globin chains: alpha and beta). The severity of the condition in this category of patients depends on the quantity of the beta-globin gene that is absent. The combined effects of S haemoglobin and shortage of beta globin result in abnormal red blood cells. 

How is sickle cell disease diagnosed?

Generally, SCD is detected by subjecting the blood to haemoglobin electrophoresis. This can be done on blood collected from any source (from adults, children or even cord blood of baby in pregnancy). Currently, genetic screening is done which help determine the type of sickle cell disease or confirm a diagnosis whenever there is ambiguity from blood test.

Diagnosis may be done in pregnancy using the sample of either tissue obtained from placenta (at 10 weeks of pregnancy) or amniotic fluid (at 15 weeks of pregnancy). This test detects the S haemoglobin gene but not the severity of the disease.

What are the complications of sickle cell disease?

The complications of sickle cell disease depend on the severity of the abnormality of haemoglobin gene involved. Those with HbSS tend to have the worst severity, followed by those with HbSC. Individuals with HbAS or HbAC do not usually manifest with symptoms while those with HbS beta thalassemia manifest symptoms based on the quantity of the beta globin gene deficiency. 

The common complications of sickle cell disease include the following:

  1. Bone pain crisis – This is the most common complications of SCD. It is due to the blockage of small blood vessels by sickle cells, depriving the tissues beyond the blockage point nutrients and oxygen as well as not allowing the metabolic waste products to be taken away.
  2. Anaemia – In persons with sickle cell disease, red blood cells die earlier than in those without it, resulting in shortage of red blood cells (anaemia). This results in a number of health challenges such as: dizziness, fast heart rate, difficulty in breathing, easy tiredness, yellowness of the eyes (jaundice), slow growth and delayed puberty. 
  3. Acute chest syndrome – This is a life-threatening complication of SCD, resulting in sudden onset of difficulty with breathing. This may be due to sickle cells blocking the blood vessels supplying the lungs, preventing blood from passing through the lungs. This may be precipitated by stress, dehydration, bacterial or viral infection, especially in children. It may present as cough, chest pain, fever and difficulty with breathing. 
  4. Blood clots inside blood vessels – Due to sluggishness of blood movement with red blood cells that become sickle shaped, the risk of blood clotting inside blood vessels (which normally should not occur) becomes very high. These blood clots can break off and lodge in the lungs, brain or heart. In any of these places, it causes life-threatening symptoms or may even lead to death. 
  5. Death of bones and joints – Sickle red blood cells can block the blood vessels supplying blood to bones and joints (which are usually tiny). Thus these bones and joints are deprived of nutrients and oxygen. If this persists for long, it can result in the death of the affected portion of bone (avascular necrosis). The hip joint is the most easily affected. 
  6. Hand and foot syndrome – This refers to the painful swelling in the hands and feet which is usually the first symptom of SCD noticed in affected child between one and three years of age. This is due to the sickle red cells blocking small blood vessels that supply the bones of the fingers and toes.
  7. Infection – People with SCD are easily prone to bacterial and viral infections. Pneumonia is very common in them and it is a leading cause of death in children. Those who require regular blood transfusion are at higher risk of blood-related infections like hepatitis. This is why a number of vaccinations have been recommended for them to reduce the risks. 
  8. Leg ulcers – Leg ulcers develop in some of them due to poor blood circulation to distant parts of the body like the feet. The ulcer may result from trauma or infection, which may delay in healing, or may occur spontaneously due to poor blood circulation.
  9. Multiple organ damage – Sickle cell disease may result in multiple organ damage, which may include liver, kidneys, heart, lungs etc, due to poor oxygen supply to them.

How can sickle cell disease be prevented?

Sickle cell disease is completely preventable. Since the disease is genetic (i.e. passed to the children by their parents), it can be prevented by genetic testing before marriage. Those with high risk of producing sickle cell disease children should not marry each other. For example, persons with SS genotype (sickle cell disease) should not marry another person with SS, AS, AC or S beta thalasaemia genotype.

Likewise persons with AS, AC and S beta thatlasaemia genotype should avoid marrying each other. Anyone with sickle cell trait or the disease should marry an individual who is completely free of the disease (HbAA)

For those who have married each other without proper screening for sickle cell disease or error in the process of confirmation, prenatal screening can be done, as earlier discussed, and the result acted on accordingly. One of the actions that may be taken is termination of pregnancy for fetuses with sickle cell disease genes.

Another one is bone marrow or stem cell transplantation. This replaces the source of the sickle red cells which can now produce normal red cells. This is not without its own complications. 

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