ALG12 encodes an alpha-1,6-mannosyltransferase that catalyzes a critical step in N-linked glycosylation by adding the eighth mannose residue to Man(7)GlcNAc(2)-PP-dolichol in the endoplasmic reticulum lumen 1. This enzymatic activity is essential for assembling the 14-sugar dolichol-linked oligosaccharide precursor that is subsequently transferred to nascent proteins by oligosaccharyltransferases 2. Biallelic ALG12 mutations cause congenital disorder of glycosylation type 1G (ALG12-CDG), characterized by impaired N-glycosylation of multiple proteins 2. Clinically, ALG12-CDG presents with broad multisystem manifestations including developmental delay, hypotonia, intellectual disability, coagulation abnormalities, recurrent infections, and dysmorphic features 1. Additional phenotypic features include skeletal dysplasia, cardiac defects, genitourinary abnormalities including hydronephrosis and multicystic kidneys, and brain anomalies 34. Phenotypic heterogeneity suggests modifying genetic and environmental factors influence disease severity 1. Beyond rare inherited disease, ALG12 dysfunction contributes to chemoresistance in intrahepatic cholangiocarcinoma through impaired N-glycosylation of ABCC1 drug transporters 5. ALG12 is also implicated in cardiac complications in carbohydrate metabolism disorders 6.