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BACKGROUND: Congenital disorders of glycosylation (CDG) are autosomal recessive disorders that produce increased serum carbohydrate-deficient transferrin (CDT) isoforms. Methods to resolve CDT from fully glycosylated transferrin (Trf) have been based on a neutral shift in the isoelectric focusing (IEF) pattern or on a reduction in the negative charge, allowing resolution by anion-exchange chromatography. Our purpose was to develop a method of resolution and relative quantification of Trf isoforms using online immunoaffinity liquid chromatography-mass spectrometry (LC-MS). METHODS: Serum (25 microL) was diluted with 100 microL of water before application to an immunoaffinity column that sequestered Trf isoforms. Trf isoforms were eluted from the immunoaffinity column, concentrated on a C4 column, eluted from the C4 column, and introduced into the mass spectrometer. Analysis of the Trf isoforms was entirely automated and completed in 100 samples analyzed in a single day. Moreover, the nature of the oligosaccharide defect in CDG is accurately reflected by mass resolution, and subtle oligosaccharide truncations may also be detected by this method.
Lacey et al. (Thu,) studied this question.