ATP9B is a P4-ATPase (Type IV P-type ATPase) that functions as a phospholipid flippase, translocating phospholipids from the exoplasmic (luminal) leaflet to the cytoplasmic leaflet of cellular membranes 12. The protein localizes exclusively to the trans-Golgi network (TGN) and operates independently of CDC50 auxiliary proteins, unlike other P4-ATPases 2. ATP9B contains a Golgi localization signal in its N-terminal cytoplasmic region that determines its specific subcellular targeting 23. Functionally, ATP9B works together with ATP9A in the exocytic pathway, facilitating transport of proteins like VSVG from the Golgi to the plasma membrane, with both proteins capable of forming homomeric and/or heteromeric complexes 1. The flippase activity of ATP9B is crucial for this transport process 1. Disease relevance includes associations with hepatocellular carcinoma risk through rare genetic variants identified in genome-wide association studies 4 and potential involvement in Alzheimer's disease susceptibility as suggested by blood biomarker analyses 5. Additionally, circular RNA derived from ATP9B (circATP9b) has been implicated in osteoarthritis progression and inflammatory responses through microRNA-mediated regulatory mechanisms 67.