â– LECTURE OVERVIEW: Lynch Syndrome (Hereditary Nonpolyposis Colorectal Cancer, HNPCC) is an autosomal dominant cancer predisposition syndrome characterized by defective DNA mismatch repair.
â– GENETIC AND BIOCHEMICAL BIOCHEMISTRY:
1. Mismatch Repair (MMR) Defect: Caused by germline mutations in DNA Mismatch Repair genes, primarily MSH2, MLH1, MSH6, and PMS2.
2. Single-Base Mispairings: During S-phase replication, DNA polymerases can accidentally introduce single-base mispairs or small insertion-deletion loops.
3. Splicing Corrections: The MMR system scans newly synthesized strands, excises mispaired bases, and resynthesizes correct sequences.
4. Microsatellite Instability (MSI): Microsatellites are short, repetitive, non-coding DNA sequences prone to polymerase slippage. When MMR is defective, these repeat lengths mutate rapidly, creating a hypermutable state termed Microsatellite Instability (MSI).
5. Two-Hit Hypothesis: Tumorigenesis occurs when the somatic wild-type allele is mutated (second-hit), driving rapid progression of colon adenomas into invasive carcinomas.
â– CLINICAL DIAGNOSTIC METRICS:
Establishing a definitive diagnosis requires combining serum biomarkers with gold-standard diagnostic modalities. High-sensitivity ELISAs are used initially to minimize false negatives, followed by highly specific confirmatory testing.
â– GERIATRIC PHYSIOLOGIC ADJUSTMENTS:
Older patients display reduced physiological reserves, altered muscle-to-fat distributions, and distinct renal filtration profiles.
[HY-BOARD-1122]
🌟 Dynamic Clinical Key:
Lynch syndrome predisposes patients to proximal (right-sided) colon cancers with a notable lack of heavy pre-existing polyposis. It is also associated with a massive lifetime risk of endometrial cancer in women, as well as ovarian, gastric, small bowel, and transitional cell urothelial tract carcinomas. Always correlate elevated serum spikes with continuous vital readings to rule out false laboratory spikes. Always adjust therapeutic doses based on age-related glomerular filtration clearance.