title: Screening using serum percentage of carbohydrate-deficient transferrin for congenital disorders of glycosylation in children with suspected metabolic disease.
abstract: 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 alpha(1)-antitrypsin (alpha(1)-AT).
  
  
  METHODS
  We performed approximately 8000 serum %CDT determinations using %CDT turbidimetric immunoassay (TIA). In selected samples, IEF analysis of Tf and alpha(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 alpha(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.
  
  
  CONCLUSIONS
  The combined use of CDT immunoassay with IEF of Tf and alpha(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.
authors.affiliation: Centro de Diagnóstico de Enfermedades Moleculares, Dpto. de Biología Molecular CBM-SO, Facultad de Ciencias, CIBER de Enfermedades Raras, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Celia
authors.initials: C
authors.lastname: Pérez-Cerdá
authors.forename: Dulce
authors.initials: D
authors.lastname: Quelhas
authors.forename: Ana I
authors.initials: AI
authors.lastname: Vega
authors.forename: Jesús
authors.initials: J
authors.lastname: Ecay
authors.forename: Laura
authors.initials: L
authors.lastname: Vilarinho
authors.forename: Magdalena
authors.initials: M
authors.lastname: Ugarte
mesh_terms: D000293:Adolescent; D002239:Carbohydrate Metabolism, Inborn Errors / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D006031:Glycosylation; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007525:Isoelectric Focusing; D008403:Mass Screening; D010949:Plasma; D011110:Polymorphism, Genetic; D020033:Protein Isoforms / Q000097:blood; D012016:Reference Values; D044967:Serum; D014168:Transferrin / Q000031:analogs & derivatives* / Q000032:analysis / Q000235:genetics; D000515:alpha 1-Antitrypsin / Q000097:blood
chemical_list: D020033:Protein Isoforms; D014168:Transferrin; D000515:alpha 1-Antitrypsin; C056759:carbohydrate-deficient transferrin