Lynch Syndrome as a Spectrum of Four Distinct Genetic Disorders: Toward Genotype-Guided Precision Management in the NGS Era.

Lynch syndrome (LS), is traditionally managed uniformly despite being caused by pathogenic variants in four distinct mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2). This approach fails to leverage gene-specific characteristics for precision healthcare delivery. This review redefines LS as four distinct genetic syndromes and establishes a genotype-guided precision management framework to optimize risk stratification, surveillance, and therapeutic interventions. We synthesized molecular, clinical, and outcomes data from the Prospective Lynch Syndrome Database (8500+ carriers; 70,000 person-years), genomic studies characterizing gene-specific mutational patterns, and immunotherapy trials while referencing international guidelines [National Comprehensive Cancer Network (NCCN), European Hereditary Tumour Group (EHTG)/European Society of Coloproctology (ESCP), and European Society for Medical Oncology (ESMO)] to formulate genotype-stratified recommendations. Fundamental molecular differences necessitate differentiated management strategies. MLH1 deficiency exhibits unique "two-in-one hit" mechanisms driving aggressive tumorigenesis with high interval cancer rates. MSH2 deficiency presents the highest tumor mutational burden (≈47 mutations per megabase; Mut/Mb) and broadest cancer spectrum. MSH6 deficiency displays distinctive high-single-nucleotide variant (SNV)/low-insertion-deletion (Indel) patterns often presenting as microsatellite instability-low (MSI-low) or microsatellite stable (MSS), complicating conventional detection. PMS2 deficiency demonstrates substantial attenuation due to redundancy. These translate into precision interventions: MLH1/MSH2 carriers require colonoscopy from age 25 at 1-2-year intervals with extended colectomy preferred, while MSH6/PMS2 carriers can defer surveillance to age 35-40 with longer intervals and undergo segmental resection. Immune checkpoint inhibitors (ICIs) are effective in deficient MMR (dMMR)/microsatellite instability-high (MSI-H) tumors across all four MMR genotypes. Genotype-specific precision management optimizes the benefit-burden balance, enhances early cancer detection, reduces overtreatment, and enables personalized genetic counseling, advancing precision healthcare for LS families and addressing critical gaps in hereditary cancer care.