Biomarker Discovery for PMM2-CDG Using Fractionated N-Glycomics Analysis.

BACKGROUND: The most common congenital disorder of glycosylation (CDG) worldwide is phosphomannomutase 2‎ (PMM2)-CDG, which presents with a highly variable, multisystem clinical spectrum that poses challenges for diagnosis and prognosis. MATERIALS AND METHODS: We performed N-glycomics analysis on plasma and 3 plasma fractions: affinity-purified transferrin, IgG, and a triple-depleted fraction in which IgG, transferrin, and albumin were removed. A total of 103 samples from 71 PMM2-CDG patients were analyzed. RESULTS: Three major glycosylation abnormalities were identified in PMM2-CDG: (a) increases in intermediate glycans derived from high-mannose glycan assembly; (b) decreases in mature/processed multi-antennary N-glycans; and (c) abnormal fucosylation and branching. Total plasma N-glycan analysis demonstrated high clinical sensitivity and specificity, with increased Man3GlcNAc2 (Man3)/Man4-6, Man3/8-9, and Man5/8 ratios detected in all patients. Novel PMM2-CDG diagnostic biomarkers were also identified from this study, including increased Man4GlcNAc2 linkage isomers in plasma and novel hybrid glycans in the transferrin fraction. When correlated with the Nijmegen Progression CDG Rating Scale (NPCRS) in a diverse cohort age >2 years (n = 39; NPCRS 10-40), 11 glycans and 10 glycan ratios from total plasma and plasma fractions showed significant associations, providing strong candidates for use as disease biomarkers for PMM2-CDG. CONCLUSIONS: We identified 35 plasma N-glycan biomarkers in a large cohort of patients with PMM2-CDG, identifying key glycans and glycan ratios that correlate with clinical severity. Utilizing fractionated N-glycan profiling enhanced these clinical correlations, demonstrating their strong prognostic value and promising application as surrogate biomarkers in clinical trials.