RABEPK (Rab9 effector protein with kelch motifs) functions as a Rab9 effector protein required for endosome to trans-Golgi network (TGN) transport, playing a critical role in vesicle docking and receptor-mediated endocytosis. The protein localizes to the cytosol, endosomes, and TGN membranes, where it mediates vesicle trafficking through protein-protein interactions. Beyond its canonical transport function, RABEPK has emerged as a genetically associated factor in complex neuropsychiatric and disease phenotypes. Genome-wide association studies identified intronic variants in RABEPK associated with opioid use disorder (OUD) in a cross-ancestry meta-analysis of 425,944 subjects 1. A separate GWAS meta-analysis of opioid addiction identified RABEPK within a significant gene cluster (SCAI/PPP6C/RABEPK) 2. Additionally, RABEPK was identified as a candidate gene in a unique family with developmental colour agnosia, suggesting potential involvement in higher-order cognitive functions 3. In cancer contexts, elevated RABEPK expression correlates with poor prognosis in colorectal cancer patients and shows association with drug resistance 4. RABEPK was also identified as a hub susceptibility gene for COVID-19 in lung adenocarcinoma patients 5 and showed differential expression patterns in response to Asian dust exposure 6. Notably, RABEPK maps within quantitative trait loci regions modulating prion disease incubation time 7, suggesting pleiotropic effects across neurological conditions.