<prompt> Sickle cell anaemia is due to:AdditionDeletionPoint mutationNone  <response>: Ans: c Point mutation Ref: Robbins, 7th ed,p. 628Sickle 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 HbAIn heterozygous state -40 chains defective i.e., HbA presentHbA a2b2 Hb A2 a2d2HbF a2g2 Most important factor which affects degree of sickling is amount of Hb S and its interaction with other Hb chainsFactors favouring polymerization Hypoxia -2,3 BPG - polymerization Acidosis - acidosis - polymerization Hb concentration -1 Hb concentration - polymerization Combination with other hemoglobins - already discussed 