A Novel N-Tetrasaccharide in Patients with Congenital Disorders of Glycosylation, Including Asparagine-Linked Glycosylation Protein 1, Phosphomannomutase 2, and Mannose Phosphate lsomerase Deficiencies

作者：Zhang Wenyue; James Philip M; Ng Bobby G; Li Xueli; Xia Baoyun; Rong Jiang; Asif Ghazia; Raymond Kimiyo; Jones Melanie A; Hegde Madhuri; Ju Tongzhong; Cummings Richard D; Clarkson Katie; Wood Tim; Boerkoel Cornelius F; Freeze Hudson H; He Miao^*

来源：Clinical Chemistry, 2016, 62(1): 208-217.

DOI：10.1373/clinchem.2015.243279

BACKGROUND: Primary deficiencies in mannosylation of N-glycans are seen in a majority of patients with congenital disorders of glycosylation (CDG). We report the discovery of a series of novel N-glycans in sera, plasma, and cultured skin fibroblasts from patients with CDG having deficient mannosylation.
METHOD: We used LC-MS/MS and MALDI-TOF-MS analysis to identify and quantify a novel N-linked tetrasaccharide linked to the protein core, an N-tetrasaccharide (Neu5Ac alpha 2,6Gal beta 1,4-GlcNAc beta 1,4GlcNAc) in plasma, serum glycoproteins, and a fibroblast lysate from patients with CDG caused by ALG1 [ALG1 (asparagine-linked glycosylation protein 1), chitobiosyldiphosphodolichol beta-mannosyltransferase], PMM2 (phosphomannomutase 2), and MPI (mannose phosphate isomerase).
RESULTS: Glycoproteins in sera, plasma, or cell lysate from ALG1-CDG, PMM2-CDG, and MPI-CDG patients had substantially more N-tetrasaccharide than unaffected controls. We observed a >80% decline in relative concentrations of the N-tetrasaccharide in MPI-CDG plasma after mannose therapy in 1 patient and in ALG1-CDG fibroblasts in vitro supplemented with mannose.
CONCLUSIONS: This novel N-tetrasaccharide could serve as a diagnostic marker of ALG1-, PMM2-, or MPI-CDG for screening of these 3 common CDG subtypes that comprise >70% of CDG type I patients. Its quantification by LC-MS/MS may be useful for monitoring therapeutic efficacy of mannose. The discovery of these small N-glycans also indicates the presence of an alternative pathway in N-glycosylation not recognized previously, but its biological significance remains to be studied.

• 出版日期2016-1