Sickle cell anemia is due to:
Sickle cell disease is a hereditary hemoglobinopathy, characterized by the defective haemoglobins.
It is caused by a point mutation at the sixth position of the beta globin chain leading to substitution of valine
residue for a glutamic acid residue. In homozygous state  -100 % chains defective i.e., no HbA In heterozygous
state  -40 % chains defective i.e., HbA present HbA = α2β2 Hb A2 = α2δ2 HbF = α2γ2 • Most important factor
which affects degree of sickling is amount of Hb S and its interaction with other Hb chains  Factors favouring polymerization ■ Hypoxia -↑2,3 BPG → ↑ polymerization
■ Acidosis - ↑ acidosis → ↑ polymerization ■ Hb concentration -1 Hb concentration →↑ polymerization ■ Combination with other hemoglobins - already discussed
Addition
Deletion
None
Point mutation