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. 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.
University Medical Center Nijmegen, Laboratory of Pediatrics and Neurology, NL-6525 GC Nijmegen, The Netherlands.
Suzan
S
Wopereis
Stephanie
S
Grünewald
Eva
E
Morava
Johannes M
JM
Penzien
Paz
P
Briones
M Teresa
MT
García-Silva
Pierre N M
PN
Demacker
Karin M L C
KM
Huijben
Ron A
RA
Wevers
D000293:Adolescent; D000367:Age Factors; D053305:Apolipoprotein C-III; D001056:Apolipoproteins C / Q000235:genetics*; D002239:Carbohydrate Metabolism, Inborn Errors / Q000175:diagnosis*; D002648:Child; D002675:Child, Preschool; D006031:Glycosylation; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007525:Isoelectric Focusing; D011134:Polysaccharides / Q000096:biosynthesis*; D020033:Protein Isoforms / Q000235:genetics; D012016:Reference Values
D053305:Apolipoprotein C-III; D001056:Apolipoproteins C; D011134:Polysaccharides; D020033:Protein Isoforms