Tumor suppressor genes and cancer

[Lothric]

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Hey,

I can read that in order for cancer to develop, one must have both alleles for a tumor suppressor gene mutated. This is apparently not true of oncogenes, according to the same source. The examples that were given were Li-Fraumeni syndrome and Lynch syndrome. But isn't Li-Fraumeni syndrome due to a mutation (observe a as in singular) in the gene coding for the tumor suppresor p53? Isn't this a paradox?

The source is First Aid 2016 (step 1) by the way.

 

[Salmanss23]

It is due to the phenomenon of dominant negative mutation .

 

[KnockKnock]

To elaborate on what Salmanss23 said - dominant negative mutation means that the recessive protein (in this case one bad p53 gene and protein product) can interfere with the remaining functional p53 protein. Thus, you essentially have reduced/minimal/no working p53 depending on the severity.

Think of dominant negative mutations as a semi-exception to the two-hit hypothesis for tumor suppressor genes.

That being said, dominant negative mutations is not a concept that is solely exclusive to cancer-genes. I believe it also plays a role in Marfan's syndrome with fibrillin mutations (and I'm sure many other diseases).

 

[Phloston]

Hey,

I can read that in order for cancer to develop, one must have both alleles for a tumor suppressor gene mutated. This is apparently not true of oncogenes, according to the same source. The examples that were given were Li-Fraumeni syndrome and Lynch syndrome. But isn't Li-Fraumeni syndrome due to a mutation (observe a as in singular) in the gene coding for the tumor suppresor p53? Isn't this a paradox?

The source is First Aid 2016 (step 1) by the way.

Throughout life we all acquire mutations in different genes. If you don't carry a congenital mutation, your allele in every cell can afford to get messed up once in the 90 some odd years you'll live, cuz there's still a healthy copy remaining. But if you have the syndrome, you'll get cancer despite having only one mutation congenitally, cuz all it takes is for one error to occur, at any age. That's why, yes, although it's a tumour suppressor gene that's mutated (and two errors are needed), carrying a mere single mutation to start with is sufficient to definitely have clinical presentation.