Overview

• SCA → caused by an autosomal recessive single gene defect in the beta chain of haemoglobin, resultin in production of sickle cell haemoglobin (HbS)
• Sickle cell trait occurs if HbS is inherited from one parent and the normal HbA from the other (sickle cell diseaese = child inherits sickle gene from each parent)
• Approx 8% of black people carry the sickle cell gene
• Typically presents after 6 months of age as the production of HbF decreases and HbS levels increase
• Sickle cell trait or disease offers a protective effect against malaria in endemic regions and this has led to positive selection for the gene mutation
• RBC’s containing HbS become rigid and distorted into a crescent shape. Glutamatic acid (polar) ****is replaced by valine (non-polar) at the sixth amino acid of the beta globin chain
• Factors precipitating sickling → infection, dehydration, hypoxia, acidosis

HbAA = normal

HbAS = carrier (sickle cell trait)

HbSS = sickle cell disease

Making Diagnosis

Clinical Features:

• Persistent pain in skeleton, chest or abdomen → vaso-occlusive crises
  • Sickle cells are fragile and haemolyse ⇒ block small blood vessels and cause infarction
  • Precipitated by infection, dehydration, deoxygenation, hypoxia (will have precipitating trigger in hx)
• Dactylitis → swollen dorsa of the hands and feet
• Splenic Sequestration (Splenomegaly) → sickle cells sequester in spleen and undergo phagocytosis. Leads to functional hyposplenism causing reduced immune function (esp. to encapsulated organisms).
• High Temperature