Sickle cell anemia is caused by which type of mutation?

Sickle cell anemia is caused by a missense mutation. A single nucleotide substitution in the beta-globin gene changes the codon GAG (glutamic acid) to GTG (valine) at position 6 of the beta-globin chain. Because a different amino acid is incorporated (valine instead of glutamic acid), this is a classic missense mutation. A nonsense mutation would introduce a premature stop codon. A sense/silent mutation would not change the amino acid. The altered protein causes RBCs to sickle under low oxygen.