The impact of mass spectrometry in the diagnosis of congenital disorders of glycosylation

Contribution of mass spectrometry (MS) in the diagnosis and characterization of congenital disorders of glycosylation (CDG) has long been known. CDG type I diseases are characterized by the under-occupancy of protein N-glycosylation sites. Electrospray (ESI) MS and matrix assisted laser desorption ionization (MALDI) MS are effective for underglycosylation analyses of intact serum Transferrin (Tf) in CDG-I patients by mass determination of individual component glycoforms. Thus, high-throughput methods developed to speed-up analytical times found increasing application in clinical testing for CDG detection. ESI MS recognizable glycoform profiles of serum Tf have been reported in CDG-I different from PMM2-CDG and in individual CDG-II defects. MALDI MS analysis of acidic and neutral N-linked glycans released from total plasma or targeted glycoproteins, is the mainstream tool to explore abnormal oligosaccharide structure and changes in the relative amount of individual oligosaccharides in CDG-II patients. Here we briefly review state-of-the-art and updates of MS-based applications for the diagnosis of CDG with special emphasis to detectable glycosylation profiles reported in different CDG types.