AP1M1 (adaptor protein complex 1 subunit μ1) is a medium chain subunit of the clathrin-associated AP-1 complex that mediates protein sorting and vesicular transport. At the trans-Golgi network (TGN) and endosomes, AP1M1 functions as part of a heterotetrameric complex that recruits clathrin to membranes and recognizes sorting signals in transmembrane cargo molecules, regulating cargo shuttling between endosomes and the TGN via clathrin-coated vesicles 1. AP1M1 is essential for proper subcellular trafficking; knockout mice demonstrate developmental arrest during mid-organogenesis 1. Recent evidence reveals AP1M1's role in modulating antisense oligonucleotide (ASO) activity by controlling endosome-to-lysosome trafficking; AP1M1 depletion increases ASO efficacy by delaying lysosomal degradation and prolonging endosomal residence time 2. AP1M1 also interacts with varicella-zoster virus tegument protein ORF9p, which is critical for viral secondary envelopment and infectivity 3. Dysregulation of AP1M1 associates with disease pathogenesis; it appears as a prognostic biomarker in osteosarcoma and lung adenocarcinoma and is identified among differentially expressed genes in schizophrenia 4, 5, 6. Mutations in AP1 subunits constitute a new disease class termed adaptinopathies 1.