Question:medium
HNPCC has defect in:
HNPCC has defect in:
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Recall which DNA repair pathway corrects replication errors and is defective in Lynch syndrome.
Updated On: Jun 23, 2026
- Nucleotide excision
- Base pair excision
- Point mutation
- Mismatch repair gene
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The Correct Option is D
Solution and Explanation
HNPCC (Hereditary Non-Polyposis Colorectal Cancer) = Lynch Syndrome. It is the most common inherited colorectal cancer, accounting for ~3-5% of all colorectal cancers.
Defect: Mismatch Repair (MMR) genes
Genes involved (germline mutations):
- $MSH2$ (most common)
- $MLH1$
- $MSH6$
- $PMS2$
- $EPCAM$
Consequence of MMR deficiency:
- Replication errors (insertions/deletions) at microsatellite sequences go uncorrected
- Results in $Microsatellite\ Instability\ (MSI-H)$
- Rapid accumulation of mutations leads to colorectal and other cancers
DNA repair mechanisms and associated syndromes:
- Nucleotide excision repair (NER) defect: Xeroderma Pigmentosa, Cockayne Syndrome
- Base excision repair (BER) defect: MUTYH-associated Polyposis
- Mismatch repair (MMR) defect: HNPCC / Lynch Syndrome
- Non-homologous end joining (NHEJ) defect: SCID
HNPCC cancers: Colorectal (most common), endometrial, ovarian, gastric, urinary tract
\[\boxed{\text{Mismatch repair gene defect (MMR)}}\]
Defect: Mismatch Repair (MMR) genes
Genes involved (germline mutations):
- $MSH2$ (most common)
- $MLH1$
- $MSH6$
- $PMS2$
- $EPCAM$
Consequence of MMR deficiency:
- Replication errors (insertions/deletions) at microsatellite sequences go uncorrected
- Results in $Microsatellite\ Instability\ (MSI-H)$
- Rapid accumulation of mutations leads to colorectal and other cancers
DNA repair mechanisms and associated syndromes:
- Nucleotide excision repair (NER) defect: Xeroderma Pigmentosa, Cockayne Syndrome
- Base excision repair (BER) defect: MUTYH-associated Polyposis
- Mismatch repair (MMR) defect: HNPCC / Lynch Syndrome
- Non-homologous end joining (NHEJ) defect: SCID
HNPCC cancers: Colorectal (most common), endometrial, ovarian, gastric, urinary tract
\[\boxed{\text{Mismatch repair gene defect (MMR)}}\]
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