text: There are several common types of nonsynonymous substitutions.
  Missense mutations are nonsynonymous substitutions that arise from point mutations, mutations in a single nucleotide that result in the substitution of a different amino acid, resulting in a change to the protein encoded.
  Nonsense mutations are nonsynonymous substitutions that arise when a mutation in the DNA sequence causes a protein to terminate prematurely by changing the original amino acid to a stop codon. Another type of mutation that deals with stop codons is known as a nonstop mutation or readthrough mutation, which occurs when a stop codon is exchanged for an amino acid codon, causing the protein to be longer than specified.