Transferrin and apolipoprotein C-III isofocusing are complementary in the diagnosis of N- and O-glycan biosynthesis defects.

Background: Apolipoprotein C-III (apoC-III) isoelectric focusing (IEF) can be used to detect abnormalities in the biosynthesis of core 1 mucin-type O-glycans.

Methods: We studied plasma samples from 55 patients with various primary defects in N- and/or O-glycosylation, 21 patients with secondary N-glycosylation defects, and 6 patients with possible glycosylation abnormalities. Furthermore, we analyzed 500 plasma samples that were sent to our laboratory for selective screening for inborn errors of metabolism.

Abnormal glycosylation with hypersialylated O-glycans in patients with Sialuria.

Sialuria is an inborn error of metabolism characterized by coarse face, hepatomegaly and recurrent respiratory tract infections. The genetic defect in this disorder results in a loss of feedback control of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine-kinase by CMP-N-acetylneuraminic acid (CMP-NeuAc) resulting in a substantial overproduction of cytoplasmic free sialic acid. This study addresses fibroblast CMP-NeuAc levels and N- and O-glycan sialylation of serum proteins from Sialuria patients.

Patients with unsolved congenital disorders of glycosylation type II can be subdivided in six distinct biochemical groups.

Defects in the biosynthesis of N- and core 1 O-glycans may be found by isoelectric focusing (IEF) of plasma transferrin and apolipoprotein C-III (apoC-III). We hypothesized that IEF of transferrin and apoC-III in combination with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of apoC-III may provide a classification for congenital disorders of glycosylation (CDG) patients. We analyzed plasma from 22 patients with eight different and well-characterized CDG subtypes and 19 cases with unsolved CDG.

A combined defect in the biosynthesis of N- and O-glycans in patients with cutis laxa and neurological involvement: the biochemical characteristics.

Based on our preliminary observation of abnormal glycosylation in a cutis laxa patient, nine cutis laxa patients were analyzed for congenital defects of glycosylation (CDG). Isoelectric focusing of plasma transferrin and apolipoproteinC-III showed that three out of nine patients had a defect in the biosynthesis of N-glycans and core 1 mucin type O-glycans, respectively. Mass spectrometric N-glycan analyses revealed a relative increase of glycans lacking sialic acid and glycans lacking sialic acid and galactose residues.

Apolipoprotein C-III isofocusing in the diagnosis of genetic defects in O-glycan biosynthesis.

Background: Defects in the biosynthesis of N-glycans may be found by isoelectric focusing (IEF) of plasma transferrin. No test is available to demonstrate O-glycan biosynthesis defects.

Methods: We used isoforms of apolipoprotein C-III (apoC-III) as a marker for the biosynthesis of core 1 mucin type O-glycans.