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Nonsense Mutations
Nonsense mutations occur when a point mutation creates a stop codon too early in a gene. As a result, protein synthesis stops before the full protein is made. This leads to a shortened (truncated) protein, which usually does not work properly or does not work at all (Alberts et al., 2015) (see Figure 2).
Because proteins often need their full structure to function correctly, nonsense mutations are usually more harmful than synonymous or neutral mutations. The missing part of the protein can remove essential functional regions, making the protein unstable or useless (Griffiths et al., 2019).
Several serious genetic diseases are caused by nonsense mutations, including Duchenne muscular dystrophy and cystic fibrosis (Strachan & Read, 2018).
Example: Cystic Fibrosis
Cystic fibrosis is caused by mutations in a gene that codes for an ion channel protein, which controls the movement of salt and water in certain tissues, especially in the lungs. When this protein does not function correctly, thick mucus builds up in the airways. This mucus makes breathing difficult and leads to frequent lung infections.
Although cystic fibrosis cannot be cured, modern treatments can help manage symptoms and improve quality of life. This example shows how a single mutation that introduces an early stop codon can have serious effects on the whole organism (National Human Genome Research Institute, 2023).