P095: March MADDness: A diagnostic dilemma with genotype/phenotype discordance

pathogenic and the other of unknown significance.Serum carbohydrate-deficient transferrin analysis was normal, but plasma N-Glycan analysis indicated increased levels of Glc3Man7GlcNAc2 and Glc3Man8, suggesting MOGS-CDG (Congenital Disorder of Glycosylation, Type IIb).Diagnostic Workup: Further testing using Liquid Chromatography High Resolutions Accurate Mass Spectrometry (LC-HRAM) confirmed the diagnosis by identifying specific N-glycan structures, including Glc3Man7-8 in IgG and an increased Glc3Man7 in a triple-depleted fraction (IgG, transferrin, albumin removed).Notably, the N-glycan profile in the patient's transferrin remained normal.MOGS-CDG results from the loss of function of mannosyl-oligosaccharide glucosidase (glucosidase I), an enzyme critical for glycoprotein quality control in the endoplasmic reticulum.