The severity of sickle cell disease varies. The disease is more severe in patients with haemoglobin SS or haemoglobin S beta thalassaemia than in those with haemoglobin S beta+ thalassaemia or haemoglobin SC disease. The Arab - Indian haplotype produces a less severe disease than the African haplotype. Similarly, the coinheritance of one or two, alpha globin chain deletions or high fetal haemoglobin level in hereditary persistence of fetal haemoglobin are associated with mild disease, The severity is therefore higher in the Sub Saharan African sub region. However, the severity of the disease varies widely for unexplained reasons among patients with haemoglobin SS in this region.