A genetic alteration in which a single base pair substitution alters the genetic code in a way that produces an amino acid that is different from the usual amino acid at that position. Some missense variants (or mutations) will alter the function of the protein. Also called missense variant.

When does a missense mutation occur?

A missense mutation occurs when there is a mistake in the DNA code and one of the DNA base pairs is changed, for example, A is swapped for C. This single change means that the DNA now encodes for a different amino acid, known as a substitution.

What is an example of a missense mutation?

For instance in sickle-cell disease, the 20th nucleotide of the gene for the beta chain of hemoglobin on chromosome 11 is changed from the codon GAG to GTG so that when translated the 6th amino acid is now a valine instead of glutamic acid. Compare: nonsense mutation.