AP3M1 encodes the mu-1 subunit of the AP-3 adaptor complex, a non-clathrin-associated complex localized to the Golgi region and peripheral structures. The protein facilitates vesicle budding from the Golgi membrane and mediates trafficking to lysosomes, working in concert with the BLOC-1 complex to target cargo into vesicles for axonal and synaptic delivery [UniProt annotation]. AP3M1 functions as a rate-limiting component of AP-3 complex assembly, with its depletion triggering decreased abundance of other complex members 1. Clinically, AP3M1 dysfunction associates with multiple pathologies. In endometriosis, AP3M1 is significantly downregulated and identified as a key diagnostic biomarker linked to programmed cell death dysregulation 2. Genome-wide Mendelian randomization analysis confirmed AP3M1 as a promising therapeutic target, showing inverse association with endometriosis risk 3. In cervical carcinomas, AP3M1 expression is reduced in 23% of tumors compared to normal tissue, often occurring alongside downregulation of other AP-3 subunits 4. Additionally, AP3M1 genetic variation associates with cardiac age acceleration, predicting earlier onset of arrhythmia, heart failure, myocardial infarction, and mortality 5. These findings indicate AP3M1 dysfunction contributes to diverse disease pathogenesis, supporting its potential as a diagnostic and therapeutic target.