YIF1B is a membrane trafficking protein that functions primarily in endoplasmic reticulum (ER) to Golgi vesicle-mediated transport and organizes these compartments 1. It localizes to the ER-Golgi intermediate compartment rather than the Golgi itself and regulates anterograde protein trafficking while facilitating proper Golgi architecture 1. YIF1B plays a critical role in targeting serotonin 5-HT1A receptors to neuronal dendrites through a vesicular scaffolding complex involving Yip1A, Rab6, and Kif5B 2. Additionally, YIF1B contributes to primary cilium and sperm flagellum assembly through protein transport 3. Dysfunction of YIF1B causes Kaya-Barakat-Masson syndrome (KABAMAS), a rare severe neurodevelopmental disorder characterized by global developmental delay, epileptic encephalopathy, microcephaly, movement disorders, visual deficits, and cerebellar atrophy 43. YIF1B knockout mice exhibit neuronal reduction, altered myelination, and primary cilium abnormalities 3. The protein's role in 5-HT1A receptor trafficking is critical for serotonin neurotransmission and antidepressant response—YIF1B expression is downregulated in depression and upregulated following fluoxetine treatment 5. YIF1B interacts with ABC transporter TAPL to facilitate its ER-to-Golgi trafficking via a salt bridge within TAPL's transmembrane domain 6. These findings establish YIF1B as essential for early post-natal neurological development and brain serotonin homeostasis.