Lectin analyses of glycoprotein hormones in patients with congenital disorders of glycosylation.
OBJECTIVE
The congenital disorders of glycosylation (CDGs) are progressive multisystemic disorders characterized by a heterogeneous deficiency of the carbohydrate moieties in various structural and circulating glycoproteins, representing a natural model for glycoprotein hormone studies. Here, we studied the carbohydrate moiety of circulating glycoprotein hormones in four patients with a clinical suspicion of CDGs.


METHODS
The diagnosis of CDG-I was confirmed in two out of the four cases by transferrin isoelectrofocusing (IEF) and/or carbohydrate-deficient transferrin (CDT) test. The carbohydrate moiety of serum endocrine-related glycoproteins was investigated by means of Ricin (immunopurified thyrotropin (TSH)) and Concanavalin A (Con-A) (TSH, follicle-stimulating hormone, alpha-subunit and thyroglobulin) lectin affinity chromatography measurement.


RESULTS
CDT concentrations were very high in the two patients with CDG-I and moderately enhanced in the remaining two. In the two CDG-I patients, Ricin analysis of immunopurified TSH showed a severe impairment of lectin binding, both before and after neuroaminidase treatment, indicating a nearly complete lack of terminal sialic acid and galactose residues. In these two cases, Con-A analysis showed a significant prevalence of firmly bound isoforms with poorly processed carbohydrate chains. In the remaining two cases with unknown CDG classification, TSH binding pattern to Ricin was modestly affected and Con-A analysis showed the prevalence of weakly bound glycoprotein isoforms.


CONCLUSIONS
The results of Ricin analyses in all four patients were consistent with the CDT test and/or serum transferrin IEF. The severe alteration of TSH binding pattern to Ricin seems to be characteristic of CDG-I. Nevertheless, TSH biological properties are not severely altered, as normal thyroid function was found in both cases.
Ferrari
M C
MC
Institute of Endocrine Sciences, University of Milan, Istituto Auxologico Italiano IRCCS and Ospedale Maggiore IRCCS, Milan, Italy.
Parini
R
R
Di Rocco
M D
MD
Radetti
G
G
Beck-Peccoz
P
P
Persani
L
L
D002239:Carbohydrate Metabolism, Inborn Errors / Q000378:metabolism*; D002675:Child, Preschool; D002846:Chromatography, Affinity; D005260:Female; D006023:Glycoproteins / Q000032:analysis*; D006031:Glycosylation; D006728:Hormones / Q000032:analysis*; D006801:Humans; D007223:Infant; D037102:Lectins; D008297:Male; D012276:Ricin; D013972:Thyrotropin / Q000097:blood / Q000302:isolation & purification
D006023:Glycoproteins; D006728:Hormones; D037102:Lectins; D013972:Thyrotropin; D012276:Ricin