- Sickle cell disease (SCD) is a genetic disorder that is caused by the presence of a mutated form of hemoglobin (hemoglobin S or HbS)
- It occurs mainly in black people manifesting early in childhood.
- In Kenya, SCD is common in Nyanza, Western, and Coastal regions
- Statistics: 5% of the world’s population carries trait genes for HB disorders (sickle-cell disease and thalassemia); globally, 3.2 million people had SCD and 43 million had sickle-cell trait in 2013; about 80% of SCD occur in sub-Saharan Africa; in 2013, SCD related globally death were 176,000; 6-9 million infants are born with SCD in Africa annually affecting 3% of births; carrier frequency of sickle-cell trait in Kenya is 28-35%.
##Pathogenesis of SCD
- Homozygous inheritance of HbS gene leads to HbS
- In HbS, valine is substituted for glutamic acid in the 6th amino acid of the β chain.
- After oxygenation, HbS becomes less soluble and forms a semisolid gel
- The semisolid gel leads to deformation of RBCs into a sickle shape at sites of low oxygen pressure.
- The sickle-shaped and inflexible RBCs adhere to vascular endothelium and plug small arterioles and capillaries leading to infarction.
- The sickle cells are destroyed in the spleen
- At the same time venous plugging predisposes the patient to thromboses
- Also due to their fragility, the mechanical trauma of circulation causes them to hemolyze.
- Bones are deformed as a result of chronic compensatory marrow hyperactivity.
## Sickle cell crisis (acute exacerbation of SCD)
- There are 3 types of sickle cell crisis: thrombotic, aplastic and hemolytic
- This crisis occurs as a result of ischemia and infarction of the bones (mostly), spleen, lungs, or kidneys.
- There is often no known reason that triggers the sickle-cell crisis but occasionally it can be elicited by fever, viral infection, and local trauma.
- One of the components of sickle-cell crisis is the aplastic crisis that occurs when marrow erythropoiesis slows during acute infection leading to acute erythroblastopenia.
##Patients who are heterozygous for HbS,
- Do not experience hemolysis or sickle-cell crisis
- They can be affected by exposure to severe hypoxic conditions and exercises
- In case of severe and sustained exercises, rhabdomyolysis and sudden death can occur
- Other problems that can occur include hyposthenuria (inability to concentrate urine), unilateral hematuria and typical renal papillary necrosis