INS and neonatal diabetes mellitus: This narrative review summarizes the genetic basis and pathogenic mechanisms of NDM, categorizing them into three major pathways: (1) ATP-sensitive potassium (KATP) channelopathies (e.g., ABCC8, KCNJ11), where gain-of-function mutations inhibit insulin secretion; (2) Transcription factor defects (e.g., GLIS3, PAX6, GATA6), which impair pancreatic development and often present with syndromic features; and (3) Endoplasmic reticulum (ER) stress-mediated β-cell apoptosis, exemplified by WFS1 mutations.