Complementarity of electrophoretic, mass spectrometric, and gene sequencing techniques for the diagnosis and characterization of congenital disorders of glycosylation

Abstract

Congenital disorders of glycosylation (CDG) are rare autosomal genetic diseases affecting the glycosylation of proteins and lipids. Since CDG‐related clinical symptoms are classically extremely variable and nonspecific, a combination of electrophoretic, mass spectrometric, and gene sequencing techniques is often mandatory for obtaining a definitive CDG diagnosis, as well as identifying causative gene mutations and deciphering the underlying biochemical mechanisms. Here, we illustrate the potential of integrating data from capillary electrophoresis of transferrin, two‐dimensional electrophoresis of N‐ and O‐glycoproteins, mass spectrometry analyses of total serum N‐linked glycans and mucin core1 O‐glycosylated apolipoprotein C‐III for the determination of various culprit CDG gene mutations. “Step‐by‐step” diagnosis pathways of four particular and new CDG cases, including MGAT2‐CDG, ATP6V0A2‐CDG, SLC35A2‐CDG, and SLC35A3‐CDG, are described as illustrative examples.

SLC35A2‐CDG: Functional characterization, expanded molecular, clinical, and biochemical phenotypes of 30 unreported Individuals

“…The majority of previously reported SLC35A2‐CDG individuals, 27 of 32 (84%; Table S1), were identified by NGS with many of those affected individuals listed in the online supplemental data of large sequencing studies (Bosch et al, ; Bruneel et al, ; Dorre et al, ; Euro, Epilepsy Phenome/Genome, & Epi, ; Kimizu et al, ; Kodera et al, ; Lelieveld et al, ; Ng et al, ; Sim et al, ; Westenfield et al, ; Winawer et al, ; Yates et al, ). This explains why the number of reported subjects cited varies among studies.…”

“…To date, molecular and clinical information on 32 individuals with de novo variants in SLC35A2 have been reported with most exhibiting neurological symptoms, especially epilepsy, developmental delay, and intellectual disability (Bosch et al, ; Bruneel et al, ; Dorre et al, ; Euro, Epilepsy Phenome/Genome, & Epi, ; Kimizu et al, ; Kodera et al, ; Lelieveld et al, ; Ng et al, ; Sim et al, ; Westenfield et al, ; Winawer et al, ; Yates et al, ). Recently, WES analysis of brain specimens from 56 individuals identified five subjects harboring somatic de novo SLC35A2 variants (Winawer et al, ).…”

Mutations in the translocon‐associated protein complex subunit SSR3 cause a novel congenital disorder of glycosylation

“…A useful and often reliable biomarker for detecting N‐linked related CDG's is the abundant serum glycoprotein, transferrin . Often referred to as carbohydrate‐deficient transferrin (CDT), an abnormal transferrin profile is frequently designated as a type I or type II, which can indicate the specific portion of the affected pathway, but usually not the specific defective protein .…”

“…1,3,4 A useful and often reliable biomarker for detecting N-linked related CDG's is the abundant serum glycoprotein, transferrin. 5,6 Often referred to as carbohydrate-deficient transferrin (CDT), an abnormal transferrin profile is frequently designated as a type I or type II, which can indicate the specific portion of the affected pathway, but usually not the specific defective protein. 5 A type I CDT profile typically results from a defect in the endoplasmic reticulum (ER) localized assembly or transfer of a lipid-linked oligosaccharide (LLO) molecule to nascent proteins.…”

“…5,6 Often referred to as carbohydrate-deficient transferrin (CDT), an abnormal transferrin profile is frequently designated as a type I or type II, which can indicate the specific portion of the affected pathway, but usually not the specific defective protein. 5 A type I CDT profile typically results from a defect in the endoplasmic reticulum (ER) localized assembly or transfer of a lipid-linked oligosaccharide (LLO) molecule to nascent proteins. 7 However, type II profiles frequently involve glycan modification in the Golgi apparatus due to abnormalities in glycan processing, trafficking of proteins or nucleotide sugars, irregularities in architecture, pH regulation, and ion transport.…”