Apolipoprotein C-III isofocusing in the diagnosis of genetic defects in O-glycan biosynthesis.
SourceClinical Chemistry, 49, 11, (2003), pp. 1839-1845
Article / Letter to editor
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Laboratory of Genetic, Endocrine and Metabolic Diseases
SubjectUMCN 2.2: Vascular medicine and diabetes; UMCN 3.1: Neuromuscular development and genetic disorders; UMCN 5.1: Genetic defects of metabolism; UMCN 5.3: Cellular energy metabolism
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. Plasma samples from patients with primary defects and secondary alterations in N-glycan biosynthesis were studied by apoC-III isofocusing. RESULTS: Age-related reference values for apoC-III were determined. Plasma samples from patients with the primary congenital disorders of glycosylation (CDG) types Ia-Ic, Ie, If, IIa, and IId all showed a normal apoC-III isofocusing profile. Plasma from two patients with CDG type IIx were tested: one showed a normal apoC-III distribution, whereas the other showed a hypoglycosylation profile. In plasma from patients with hemolytic uremic syndrome (HUS), a hypoglycosylation profile was obtained. CONCLUSIONS: IEF of apoC-III is a rapid and simple technique that may be used as a screening assay for abnormalities in core 1 mucin type O-glycans. Evidence that a patient in this study has a primary genetic defect affecting both N- and O-glycosylation provides the first example of an inborn error of metabolism affecting the biosynthesis of core 1 mucin type O-glycans. Our data narrow the options for the position of the primary defect in this patient down to a step in the biosynthesis, activation, or transfer of galactose or N-acetylneuraminic acid to both N- and O-glycans. Circulating neuraminidase excreted by Streptococcus pneumoniae caused the high percentage of asialo apoC-III in two HUS patients.
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