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.
Institute of Endocrine Sciences, University of Milan, Istituto Auxologico Italiano IRCCS and Ospedale Maggiore IRCCS, Milan, Italy.
M C
MC
Ferrari
R
R
Parini
M D
MD
Di Rocco
G
G
Radetti
P
P
Beck-Peccoz
L
L
Persani
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