Medical Definition of Nonsense mutation

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Nonsense mutation: A mutation (a change) in a base in the DNA that prematurely stops the translation (reading) of messenger RNA (mRNA) resulting in a polypeptide chain that ends prematurely and a protein product that is truncated (abbreviated) and incomplete and usually nonfunctional.

The nonsense mutation converts a codon (a triplet of bases) that encodes an amino acid into a stop codon, one that specifies the termination of translation. There are three nonsense codons (UAG, UAA, and UGA) in mRNA. One of them comes normally at the end of each polypeptide. A nonsense codon is a stop codon which is out of place.

Catching such a defective messenger RNA (mRNA) before a truncated and potentially harmful protein is synthesized is the job of what is called the nonsense-mediated mRNA decay (NMD) pathway.

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Last Editorial Review: 1/25/2017

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