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The human genome contains a pair of genes for β-globin; in people with sickle cell disease, both genes are affected and the erythropoietic cells in the bone marrow will only create HbS. In people with sickle cell trait , only one gene is abnormal; erythropoiesis generates a mixture of normal HbA and sickle HbS.
Autosomal dominant A 50/50 chance of inheritance. Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition. [1]
The sickle cell trait provides a survival advantage against malaria fatality over people with normal hemoglobin in regions where malaria is endemic. The trait is known to cause significantly fewer deaths due to malaria, especially when Plasmodium falciparum is the causative organism.
The pathogen that causes the disease spends part of its cycle in the red blood cells and triggers an abnormal drop in oxygen levels in the cell. In carriers, this drop is sufficient to trigger the full sickle-cell reaction, which leads to infected cells being rapidly removed from circulation and strongly limiting the infection's progress.
Sickle-cell disease was the genetic disorder to be linked to a mutation of a specific protein. Pauling introduced his fundamentally important concept of sickle cell anemia as a genetically transmitted molecular disease. [20] This vein (4) shows the interaction between the malaria sporozoites (6) with sickle cells (3) and regular cells (1).
Some hemoglobin variants, such as HbS which causes sickle-cell anemia, are responsible for severe diseases and are considered hemoglobinopathies. Other variants cause no detectable pathology, and are thus considered non-pathological variants. [4] [5]