Hey There!
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Sickle cell anemia is a disease of red blood cells that causes them to become sickle-shaped rather than being disc-shaped, resulting from the point mutation of a single nucleotide(Arginine replaced by Thymine) which causes replacement of polar glutamate with non-polar valine at SIXTH position in the β subunit of "Hemoglobin A". Sickle cell anemia is a part of hemoglobinopathies which are a group of genetic disorders caused by the production of the structurally abnormal hemoglobin molecule, synthesis of insufficient quantities of normal hemoglobin or rarely both.
Sickle cell anemia is an autosomal-recessive disorder, which means it occurs when two mutant genes are inherited from parents that code for the synthesis of β globin chains. Keep in mind that the infant does not begin to show sickle cell symptoms because there is a large amount of hemoglobin F present in an infant and HbS or HbA(adult hemoglobin) are yet to replace HbF. In sickle cell, the life of RBCs reduces to less than 20 days thus it causes anemia.
There are 2 types of sickle cell,
- Heterozygous, which have one normal and one sickle cell gene, so RBCs show both HbS and HbA(which is normal adult Hb) and these individuals have sickle cell trait
- H.om.ozygous, which have both genes mutated and show clinical symptoms(anemia, "crises" pain, hyperbilirubinemia, infections, splenic and renal dysfunction, acute chest syndrome, stroke, bone marrow hyperplasia)
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Despite sickle cell's damaging effects in a h.om.ozygous state, suggests that a selective advantage exists for heterozygous individuals. Its prime example is heterozygous sickle cells that are less susceptible to severe malaria caused by the parasite Plasmodium falciparum.
The organism spends an obligatory part of its life cycle in the RBC. One theory suggests that these cells which are heterozygous for HbS, like those h.om.ozygous HbS, have a shorter life span than normal RBCs. The parasite cannot complete the intracellular stage of its development.
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In my opinion, the mutation is both, harmful and helpful. Harmful because the frequency of sickle cell trait increased in the regions of Africa which caused more individuals to have sickle cell anemia thus it started growing, also the individuals who had h.om.ozygous had the lowest chance of surviving malaria.Helpful in the way that malaria was once, one of the major deadliest diseases in Africa, but the heterozygous sickle cell helped people to survive there.
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Best Regards,
'BORZ'