Diagnosis of Congenital Disorders of Glycosylation Type II Subtypes Through Comprehensive N-Glycan Profiling by Mass...

Congenital disorders of glycosylation (CDG) are a group of inherited metabolic diseases rapidly growing due to the discovery of new subtypes. As with many genetic conditions, their diagnosis can be challenging, impairing proper patient care and causing additional suffering to patients and their families. We have developed an N-glycomics strategy that can provide insightful information towards diagnosing CDG type II (CDG-II). N-glycans released from the plasma of healthy individuals were labeled with deuterated iodomethane, mixed with samples from known or suspected CDG-II individuals, which were derivatized with standard iodomethane, and analyzed by liquid chromatography-mass spectrometry. After identification, relative quantification of 65 glycans was performed, revealing considerable alterations in the N-glycome of several patients. Notably, reduced fucosylation was observed in patients with FUT8-CDG and SLC35C1-CDG. Additionally, individuals with mutations in the MAN1B1 gene exhibited increased amounts of hybrid and oligomannosidic structures, whereas patients with the Golgi homeostasis disorders COG1-CDG and ATP6V0A2-CDG presented marked increases in hypogalactosylated and hyposialylated structures. Multivariate statistical analysis indicated two undiagnosed patients with alterations similar to ATP6V0A2-CDG patients and another two with a profile similar to MAN1B1-CDG patients. Genetic sequencing (targeted gene panel or whole exome sequencing) of these undiagnosed patients revealed variants in the corresponding genes, confirming the diagnosis obtained from the N-glycomics analysis. Our results demonstrate how the analysis of total plasma N-glycans can be used to identify metabolic disorders and diagnose conditions based on their molecular effects on the glycoproteome.