Sickle cell trait patient do not have manifestations as that of Sickle cell disease, because:
In Sickle cell trait, the patient is heterozygous and only one parent contributes the abnormal S gene. in each cell of these patients approximately 40% of the hemoglobin is HbS. The rate of sickling is influenced by the intracellular concentration of hemoglobin S and by the presence of other hemoglobins within the cell. In Sickle cell trait the low level of HbS is insufficient to produce sickling unless there is profound hypoxia. Sickle cell disease is an autosomal recessive disorder in which an abnormal hemoglobin leads to chronic hemolytic anemia with numerous clinical consequences. It is caused by a single DNA base change leading to an amino acid substitution of valine for glutamine in the sixth position on the beta-globin chain. In Sickle cell disease patients are homozygous and 80% of their hemoglobin is HbS. Hemoglobin S is unstable and polymerizes in the setting of various stressors, including hypoxemia and acidosis, leading to the formation of sickled red blood cells. Ref: Rosen's Emergency Medicine - Concepts and Clinical Practice By John Marx page 1597. Core Topics in Paediatric Anaesthesia edited by Ian James, page 67. Linker C.A., Damon L.E., Damon L.E., Andreadis C. (2013). Chapter 13. Blood Disorders. In M.A. Papadakis, S.J. McPhee, M.W. Rabow, T.G. Berger (Eds), CURRENT Medical Diagnosis & Treatment 2014.
50% HbS is required for occurrence of sickling
HbA prevents sickling
50% sickles
HbA prevent polymerization of Hbs