How many nucleotides in the sickle cellgene got changed?

In sickle cell disease, a single nucleotide change occurs in the beta-globin gene (HBB), where adenine (A) is replaced by thymine (T) at the sixth codon. This results in the substitution of valine for glutamic acid in the hemoglobin protein. Therefore, only one nucleotide change leads to the sickle cell mutation.