COMMD4 is a scaffold protein in the Commander endosomal recycling complex, essential for tissue homeostasis and genomic stability. As a core component of the CCC subcomplex, COMMD4 coordinates SNX17-dependent recycling of hundreds of integral membrane proteins containing ΦxNPxY/F sorting motifs from endosomes to the cell surface 1. Beyond its recycling function, COMMD4 regulates chr15 remodeling at DNA double-strand breaks by protecting histone H2B from RNF20/40-mediated monoubiquitination, enabling timely repair through both non-homologous-end-joining and homologous recombination pathways 2. COMMD4 also activates PI3K-AKT signaling by binding PI3K-p85 to release the catalytic p110 subunit 3. Clinically, COMMD4 mutations cause Ritscher-Schinzel syndrome, a recyclinopathy characterized by cerebellar, cardiac, craniofacial, and multi-organ developmental abnormalities 14. Conversely, elevated COMMD4 expression drives cancer progression in non-small cell lung cancer, glioma, and melanoma, promoting cell proliferation, migration, invasion, and drug resistance 563. In amyotrophic lateral sclerosis, COMMD4 upregulation induces neuronal ferroptosis by inhibiting the hephaestin-ferroportin iron efflux pathway, disrupting Cu-Fe homeostasis 7. COMMD4 thus represents a bifunctional protein: loss-of-function causes developmental disease through impaired endosomal recycling, while gain-of-function drives cancer and neurodegeneration.