MEDizzy - A 53-year-old man sees his family physician with concerns

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NUCLEIC ACID

A 53-year-old man sees his family physician with concerns that his skin is ‘‘bronzing.’’ He is found to have diabetes as well as an elevated ferritin level (a sign of iron overload). The physician suspects hemochromatosis and confirms the diagnosis with genetic testing. It is found that the patient’s DNA carries a mutation in which tyrosine is substituted for cysteine at position 282 (C282Y) within the HFE gene. What word below best describes this type of mutation?

ExplanationA missense mutation results from a nucleotide change within the DNA, which results in a change in the meaning of the codon, such that a different amino acid is placed within the protein. This is the case of the C282Y mutation in hereditary hemochromatosis. A silent mutation does not result in an amino acid change, by definition, owing to the degenerate nature of the genetic code, even though there has been a base change in the DNA (e.g., UUU and UUC both code for phenylalanine). A frameshift mutation, as in Duchenne muscular dystrophy, can result in premature termination of protein synthesis with a dysfunctional protein and requires either the insertion or deletion of 1 base or more. A nonsense mutation is a single base change that converts a codon to a stop codon, leading to premature termination of protein synthesis.