Microsatellite instability (MSI) is the condition of genetic hypermutability that results from impaired DNA mismatch repair (MMR). The presence of MSI represents phenotypic evidence that MMR is not functioning normally. Is the probability of finding MSI higher after radiation?
A single dose of radiation can create MMR mutants, say in Bacteria. In normal human cells a very high single dose 'may' render MMR dysfunctional, but there can be redundancy in repair of DNA damage. In colorectal cancer cells (such as derived from Lynch syndrome or HNPCC), MMR is already compromised. So when these cells will be subjected to radiation, MSI would be expected to increase, because of lack of appropriate repair. Whether, these radiations would add to MMR dysfunction, will mandate testing MMR genes for new mutations.
It would also be arduous to look for such new mutations in MMR genes. May be search hotspot regions(?).
Hope this helps..
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