OSBPL9 (Oxysterol Binding Protein Like 9) functions as a lipid transfer protein that mediates phospholipid exchange between cellular organelles. It forms a heterodimer with OSBPL11 that localizes at ER-trans-Golgi membrane contact sites and exchanges phosphatidylserine for phosphatidylinositol-4-phosphate between these organelles, a critical step in sphingomyelin synthesis 1. OSBPL9 belongs to a large family of lipid transport proteins and interacts with various cellular partners including OSBP, LRP1, and CREB3, suggesting involvement in multiple cellular processes including N-glycosylation pathways 2. Disease relevance is emerging, with homozygous nonsense variants causing severe fetal malformations including cerebral ventriculomegaly, cerebellar hypoplasia, and arthrogryposis multiplex in an autosomal recessive pattern 3. OSBPL9 shows altered expression in multiple cancers, being downregulated in liver cancer 4 and identified as a potential tumor antigen for bladder cancer mRNA vaccines 5. Additionally, it has been identified as a prognostic biomarker in colorectal cancer 6 and appears to play a role in ferroptosis-related pathways in endometriosis 7. The protein's involvement in viral infections is also suggested through interactions with flavivirus NS5 proteins 8.