TUSC3 is a multifunctional protein operating at the intersection of protein glycosylation and magnesium homeostasis with significant implications for both developmental and neoplastic disease. As an accessory subunit of the endoplasmic reticulum oligosaccharyl transferase (OST) complex, TUSC3 catalyzes N-linked glycosylation of specific protein substrates 1, particularly those with acceptor sites near cysteine residues where it forms transient mixed disulfides to facilitate glycosylation 1. Beyond its oxidoreductase function, TUSC3 critically regulates ER magnesium homeostasis through complex formation with ERMA, a mechanism essential for neuronal function and synaptic integrity 2. Dysfunction of TUSC3 manifests distinct phenotypes depending on tissue context. Loss of TUSC3 causes autosomal recessive intellectual disability through ER MgΒ²βΊ depletion and PERK-eIF2Ξ± pathway activation, leading to impaired learning, memory, and social behavior 2. In hepatocellular carcinoma, TUSC3 downregulation paradoxically promotes epithelial-mesenchymal transition and tumor progression via the LIPC/AKT axis 3, whereas in colorectal cancer, increased TUSC3 expression drives oncogenic signaling through WNT/Ξ²-catenin and MAPK pathways 4. Biliary atresia susceptibility involves TUSC3 variants affecting ciliogenesis 5. These tissue-specific roles suggest TUSC3 represents a functionally dual gene with context-dependent tumor suppressive and tumor-promoting activities. Magnesium supplementation shows therapeutic promise for TUSC3-associated intellectual disability 2, and epigenetic activation of TUSC3 may treat XMEN disease 6.