Cholestasis encompasses a broad spectrum of hepatobiliary disorders characterized by impaired bile formation or flow. Historically classified based on clinical onset and severity, the landscape of cholestatic liver disease has been revolutionized by the advent of high-throughput genomic technologies. This review elucidates the critical role of genetics in redefining the pathophysiology, diagnosis, and management of cholestasis, framing pediatric Progressive Familial Intrahepatic Cholestasis (PFIC) and Adult-Onset Cholestatic Disease (AOCD) as a continuous phenotypic spectrum. We discuss the expansion of the molecular nosology to include 13 distinct PFIC types, highlighting how defects in canalicular transporters, tight junctions, and nuclear receptors underpin clinical heterogeneity. Furthermore, we examine the paradigm shift in the diagnostic flowchart, where Next-Generation Sequencing (NGS) has largely superseded liver biopsy for etiological definition. Finally, we address the therapeutic implications of this molecular precision, demonstrating how specific genotypes dictate eligibility for novel targeted therapies, such as IBAT inhibitors, marking the transition from supportive care to personalized medicine.
