Sickle Cell Disease
An inherited haemoglobinopathy in which deoxygenated haemoglobin S polymerises, making red cells rigid and adhesive; vaso-occlusion causes ischaemic pain while haemolysis causes chronic anaemia and progressive organ damage.
Definition
Sickle cell disease is a group of inherited beta-globin disorders in which haemoglobin S, alone or paired with another abnormal beta-globin variant, causes chronic haemolysis, vaso-occlusion and progressive organ damage. Sickle cell trait, one HbS gene alongside one normal gene, is not sickle cell disease.
First principles
HbS polymerisation ties tissue injury to oxygen tension
Sickle cell disease is caused by inherited beta-globin variants that produce haemoglobin S (HbS). When deoxygenated, HbS polymerises into rigid rods that distort the red cell. Repeated sickling damages the membrane and makes the cell adhesive, so hypoxia, dehydration, cold, infection and acidosis all precipitate vaso-occlusion. Fetal haemoglobin (HbF) blocks polymerisation, which is why infants are protected for their first few months, and why raising HbF is therapeutic.
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