Received on June 15, 2007
Accepted on October 26, 2007

Molecular Diagnostics and Genetics

Screening Using Serum Percentage of Carbohydrate-Deficient Transferrin for Congenital Disorders of Glycosylation in Children with Suspected Metabolic Disease

¹ Centro de Diagnóstico de Enfermedades Moleculares, Dpto. de Biología Molecular CBM-SO, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain, CIBER de Enfermedades Raras
² Medical Genetic Institute, Clinical Biology Department, Porto, Portugal

^* To whom correspondence should be addressed. E-mail: mugarte{at}cbm.uam.es.

BACKGROUND: Diagnoses of congenital disorders of glycosylation (CDG) are based on clinical suspicion and analysis of transferrin (Tf) isoforms. Here we present our experience of CDG screening in children with a suspected metabolic disease by determination of serum percentage of carbohydrate-deficient transferrin (%CDT) in tandem with isoelectric focusing (IEF) analysis of Tf and ₁-antitrypsin (₁-AT).

METHODS: We performed approximately 8000 serum %CDT determinations using %CDT turbidimetric immunoassay (TIA). In selected samples, IEF analysis of Tf and ₁-AT was carried out on an agarose gel (pH 4–8) using an electrophoresis unit. The isoforms were detected by Western blotting and visualized by color development. We performed neuraminidase digestion of serum to detect polymorphic variants of Tf.

RESULTS: We established a cutoff value for serum %CDT of 2.5% in our pediatric population. Sixty-five patients showed consistently high values of serum %CDT. In accordance with Tf and ₁-AT IEF profiles, enzyme assays, and mutation analysis, we made the following diagnoses: 23 CDG-Ia, 1 CDG-Ib, and 1 conserved oligomeric Golgi 1 (COG-1) deficiency. In addition, we identified 13 CDG-Ix non Ia, non-Ib; 3 CDG-Ix; and 9 CDG-IIx cases, albeit requiring further characterization; 9 patients with a secondary cause of hypoglycosylation and 6 with a polymorphic Tf variant were also detected.

CONCLUSION: The combined use of CDT immunoassay with IEF of Tf and ₁-AT is a useful 1st-line screening tool for identifying CDG patients with an N-glycosylation defect. Additional molecular investigations must of course be carried out to determine the specific genetic disease.