Congenital disorders of glycosylation (CDG) constitute an ever-growing group of genetic diseases affecting the glycosylation of proteins. CDG individuals usually present with severe multisystem disorders. MAN1B1-CDG is a CDG with nonspecific clinical symptoms such as intellectual deficiency and developmental delay. Although up to 40 affected individuals were described so far, its final diagnosis is not straightforward using common biochemical methods due to the trace-level accumulation of defective glycan structures. In this study, we present three unreported MAN1B1-CDG individuals and propose a decision tree to reach diagnosis using a panel of techniques ranging from exome sequencing to gel electrophoresis and mass spectrometry. The occurrence of MAN1B1-CDG in patients showing unexplained intellectual disability and development delay, as well as a particular transferrin glycosylation profile, can be ascertained notably using matrix assisted laser desorption/ionization - time of flight (MALDI-TOF) mass spectrometry analysis of endo-β-acetylglucosaminidase H-released serum N-glycans. In addition to reporting new pathogenic variants and additional clinical signs such as hypersialorrhea, we highlight particular biochemical features of MAN1B1-CDG with potential glycoprotein-specific glycosylation defects.
Keywords: 2-DE, two-dimensional electrophoresis; A1AT, α1-antitrypsin; ApoC-III, apolipoprotein C-III; BMI, body mass index; CDG; CDG, congenital disorder(s) of glycosylation; CE, capillary electrophoresis; DD, developmental delay; DWI, Diffusion-weighted imaging; ER, endoplasmic reticulum; ESI-QTOF, electrospray ionization – quadrupole time of flight; Endo H, endo-ß-N-acetylglucosaminidase H; FLAIR, fluid-attenuated inversion recovery; HPLC, high performance liquid chromatography; Hpt, haptoglobin; Hypersialorrhea; ID, intellectual disability; Intellectual disability; M6, Man6GlcNAc2; M8A/B/C, Man8GlcNAc2 lacking the first/middle/third terminal mannose; M9, Man9GlcNAc2; MALDI-TOF, matrix assisted laser desorption/ionization – time of flight; MAN1B1; MRI, magnetic resonance imaging; MS, mass spectrometry; Man, mannose; N-glycan mass spectrometry; PNGase F, peptide-N-glycosidase F; Trf, transferrin; WES, whole exome sequencing.
© 2021 The Authors. Published by Elsevier Inc.