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Congenital disorders of glycosylation, (CDG), also known as
carbohydrate deficient glycoprotein syndromes, are a collection of disorders in
which many glycoproteins are deficient or have reduced carbohydrate side chains.
Many subtypes of congenital disorders of glycosylation have been described based
on the isoelectric focusing patterns of transferrin and on clinical features.
Enzyme deficiencies have been reported in at least four of the subtypes: Type Ia,
phosphomannomutase; Type Ib, phosphomannose isomerase; Type Ic,
glucosyltransferase; Type II, glucosamine-transferase; Type IV,
mannosyltransferase.Sialic acid is the terminal sugar residue of the two
carbohydrate side chains of transferrin. Any block in the synthesis of these
side chains will result in an undersialylated transferrin molecule. Because it
is a major serum protein and is easily detectable, transferrin is utilized as a
marker in screening for congenital disorders of glycosylation.
Enzyme analysis for CDG Ia/Ib as well as
mutation analysis for CDG Ia, Ib, and
Ic are also available from the biochemical laboratory.
Although many congenital disorders of glycosylation are yet to be described, CDG may be
suspected in patients with one or more of the following:
- Failure to thrive
- Hypotonia
- Inverted nipples
- Unusual fat deposits
- Mental and psychomotor retardation
- Stroke-like episodes
- Protein losing enteropathy
- Hypoglycemia
- Generalized dysmyelinization
- Optic atrophy
Specimen requirements: Transferrin analysis for
carbohydrate deficient glycoprotein syndromes is performed on serum. Obtain 1 ml
serum from a red top blood collection tube.
Transport: Serum must be frozen and sent on dry ice.
Standard of analysis: Qualitative analysis of
transferrin isoforms will be done by capillary electrophoresis.
Time required: Analysis will be complete within one
week.
Report: Written reports will be mailed, and when
abnormalities exist, a report will be given by telephone. If an abnormal isoform
is detected, the percentage of isoforms in relation to tetrasialotransferrin
will be reported. Reports may be sent by FAX or email if requested.
CPT Code: 82373
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