<p>Type 2 diabetes mellitus develops when insulin resistance raises insulin demand and pancreatic beta cells fail to sustain insulin supply. Genome-wide association studies support a polygenic architecture and enrich for loci that affect beta cell stimulus secretion coupling and secretory stress responses. Polygenic risk scores summarize liability across many variants and guide genetic stratification in cohort studies. This review uses TCF7L2 and CDKAL1 as two mechanistically interpretable loci to connect inherited variation to measurable physiology. TCF7L2 risk alleles reduce incretin potentiation of insulin secretion after oral nutrient exposure, which blunts early postprandial insulin release. CDKAL1 risk alleles impair the ms2 modification of t6A37 at position 37 of tRNALys(UUU), which increases proinsulin mistranslation and raises endoplasmic reticulum stress in beta cells. These defects converge during repeated postprandial cycles that require rapid insulin synthesis and secretion. Reduced incretin signaling prolongs glycemic excursions and increases secretory workload, which intensifies folding stress when translation quality control is limited. The model predicts earlier postprandial dysglycemia under obesity or aging related insulin resistance and faster loss of beta cell reserve when both pathways constrain supply. The framework supports mechanistic phenotyping and pharmacogenetic testing within a broader polygenic risk setting.</p>