Mass spectrometry (MS) of large molecules such as proteins and oligosaccharides has not been employed in clinical practices, while that of small metabolites is widely used for the screening and diagnosis of various congenital diseases. Congenital disorders of glycosylation (CDG) is a newly recognized group of diseases derived from defects in the biosynthetic pathway of protein glycosylation and the patients are never decisively diagnosed unless the glycoprotein molecules are analyzed. We have constructed a diagnostic system where MS of glycoproteins and glycopeptides identifies abnormalities in their glycan moieties. This program is anticipated to reveal the prevalence of CDG and to demonstrate the essential role of MS in the emerging field of medicine, disease glycomics and glycoproteomics.

Keywords: glycoproteins, congenital disorders of glycosylation, glycomics, proteome