title: Erythrocyte galactose 1-phosphate quantified by isotope-dilution gas chromatography-mass spectrometry.
abstract: BACKGROUND
  Measurements of alpha-D-galactose 1-phosphate (Gal-1-P) in erythrocytes are used to monitor the adequacy of dietary therapy in the treatment of galactosemia. We have devised a gas chromatography-mass spectrometry (GC/MS) isotope-dilution method for quantification of Gal-1-P.
  
  
  METHODS
  We prepared trimethylsilyl (TMS) derivatives and used alpha-D-[2-(13)C]Gal-1-P as the internal standard for GC/MS. Results obtained with this method were compared with those determined by the established enzymatic method for samples from 23 healthy individuals (11 children and 12 adults), 9 suspected patients with galactosemia, 12 galactosemic patients on diet therapy, and 2 newly diagnosed toxic neonates.
  
  
  RESULTS
  The method was linear up to 2.5 mmol/L with a lower limit of detection of 2.1 nmol (0.55 mg/L). Intra- and interassay imprecision (CVs) was 2.2-8.8%. In the 23 healthy individuals, values ranged from nondetectable to 9.2 micromol/L (2.4 mg/L of packed erythrocytes). Galactosemic patients on diet therapy had values of 10.9-45 mg/L of packed erythrocytes, whereas the newly identified patients had values of 166 and 373 mg/L.
  
  
  CONCLUSIONS
  The GC/MS method is precise and useful over the wide range of concentrations needed to assess the galactose burden in patients with galactosemia.
authors.affiliation: Metabolic Research Laboratory and. Metabolic Diagnostic Laboratory, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Claire
authors.initials: C
authors.lastname: Yager
authors.forename: Robert
authors.initials: R
authors.lastname: Reynolds
authors.forename: Michael
authors.initials: M
authors.lastname: Palmieri
authors.forename: Stanton
authors.initials: S
authors.lastname: Segal
mesh_terms: D000328:Adult; D002648:Child; D002675:Child, Preschool; D002849:Chromatography, Gas; D004912:Erythrocytes / Q000737:chemistry*; D005260:Female; D005693:Galactosemias / Q000097:blood / Q000175:diagnosis / Q000178:diet therapy; D005695:Galactosephosphates / Q000097:blood*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D015997:Neonatal Screening; D011786:Quality Control; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013403:Sugar Phosphates / Q000097:blood / Q000302:isolation & purification
chemical_list: D005695:Galactosephosphates; D013403:Sugar Phosphates; C029973:galactose-1-phosphate