N-linked protein glycosylation in eukaryotes requires the assembly of lipid-linkedoligosaccharide (LLO) precursor Glc3Man9GlcNAc2-pyrophosphate-dolichol (Glc3Man9Gn2-PDol) in the ER []. Mannosyltransferase ALG9 is a lumen-oriented glycosyltransferase required to add two different alpha-1,2-linked mannose residues at two different steps of lipid-linked oligosaccharide biosynthesis [].Mutations in the ALG9 gene cause congenital disorder of glycosylation 1L (CDG1L), a rare autosomal recessive syndrome characterised by severe skeletal dysplasia, facial dysmorphic features, polycystic kidney disease and other visceral malformations [].
