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– IMMUNOLOGICAL & CYTOKINE SIGNALLING FLUX:
Pathogen exposure or cellular distress triggers antigen-presenting cell activation. This results in the release of pro-inflammatory cytokines (such as IL-1, TNF-alpha, and IL-6) and triggers receptor-mediated cellular chemotaxis.
â– SECONDARY PREVENTION METRICS:
Implementing long-term dietary adaptations, physical therapy, and compliance aids reduces the rate of recurring acute crises by more than half.
[HY-BOARD-1236]
🌟 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. Target specific monoclonal antibodies or immune suppressors to control the hyper-inflammatory cascade. Patient education regarding warning signs and therapy adherence is the cornerstone of secondary prevention.