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A 42-year-old woman sees her physician for an annual medical examination. She mentions that her 48-year-old brother has recently been diagnosed with colon cancer. Further family history reveals a maternal uncle who died of colorectal cancer in his 50's. The physician suspects familial polyposis, but the brother's medical record shows no evidence of this. Mutation testing on the brother identifies a mutation in MLH1, a mismatch repair gene. What characteristic associated with this mutation is likely to be noted in the tumor cell DNA from her brother?
A. Active transcription of the telomerase gene
B. Dinucleotide repeat instability
C. Highly methylated CG sequences
D. Increase in euchromatin
E. Large segment deletions
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can somebody have a nice try?
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anyone heard of microsatellite instabilities?? these are very small base sequence repeats that are often mismatched and the job oh hmsh2 and hmlh1 is to check that ....
so ans shd be B
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Hi, CD45, you are correct.
The answer is B. The brother most likely has hereditary nonpolyposis colon cancer (HNPCC). Microsatellite instability is characteristic of individuals with loss-of-function mutations in the mismatch repair genes (hMLH, hMSH) associated with hereditary nonpolyposis colorectal cancer (HNPCC), hereditary endometrial cancer, and microsatellite instability in the tumor cells. Areas of DNA with dinucleotide repeats (an example of microsatellites) are often associated with strand slippage during DNA replication that can change the number of repeats on the newly synthesized strand (microsatellite instability). The mismatch repair enzymes normally correct this replication error.
Active transcription of the telomerase gene (choice A), and increase in euchromatin (choice D) are both characteristics of many tumor cells, but are not known to be specifically related to loss of mismatch repair and HPNCC.
Highly methylated CG sequences (choice C) are typically associated with silencing certain gene regions; such methylation is not a prominent mechanism related to tumorigenesis.
Large segment deletions (choice E) are associated with unequal crossovers during meiosis. A large segment deletion might result in a genetic deficiency or loss of a tumor suppressor gene, and a hereditary form of cancer. The mechanism is not strongly associated with a defective mismatch repair system.
