Sickle cell disease (also known as HbS disease)

 

Clinical features

The common features include:

  1. Anaemia
  2. Failure to thrive
  3. Repeated infections
  4. Painful swelling of the hands or feet
  5. Infarction
  6. Asplenia
  7. Abdominal pain
  8. Chest pain
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Genetics

  1. Haemoglobin contains two α-globin chains and two β-globin chains. Each individual has two copies of the β-globin gene, one from each parent.
  2. Sickle cell disease is caused by a mutation in both copies of the β-globin genes resulting in changes to the structure of the β-globin chain of haemoglobin, ie a haemoglobin variant. This results in red blood cells that form an irreversible sickle shape after repeated cycles of deoxygenation.
  3. Individuals with sickle cell disease usually have chronic anaemia due to increased destruction of red blood cells.
  4. They may also experience sickle cell crises due to blockage of blood vessels by these cells, causing bone and chest pain and damage to other organs.
  5. They usually autosplenectomise within the first ten years of life.
  6. Individuals with sickle cell disease who have crises require medical management, which may include regular blood transfusions.
  7. Sickle cell trait (term to describe the carrier state) is caused by a mutation in one copy of the β-globin gene. Carriers are usually healthy. In some very rare instances (eg anaesthesia or long distance air travel), the red blood cells of a carrier can undergo partial sickling.
  8. Sickle cell disease is an autosomal recessive condition. Carriers have a 50% chance of passing the mutated gene to their children. Couples who are both carriers have a 25% chance of having an affected child. This risk applies for every pregnancy of that partnership.
  9. Co-inheritance of sickle cell trait (or other haemoglobin variant) and β-thalassaemia minor may result in a form of sickle cell disease. This is known as compound heterozygosity, as the two types of gene mutations are different.
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