title: Definitive diagnosis of mitochondrial neurogastrointestinal encephalomyopathy by biochemical assays.
abstract: BACKGROUND
  Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the gene encoding thymidine phosphorylase (TP). The clinical manifestations of MNGIE are recognizable and homogeneous, but in the early stages, the disease is often misdiagnosed. This study assesses the reliability of biochemical assays to diagnose MNGIE.
  
  
  METHODS
  We studied 180 patients with clinical features suggestive of MNGIE, 14 asymptomatic TP mutation carriers, and 20 controls. TP enzyme activity in the buffy coat was determined by a fixed-time method, and the plasma nucleosides thymidine (dThd) and deoxyuridine (dUrd) were assessed by a gradient-elution reversed phase HPLC method. TP was sequenced through standard procedures in patients who met the clinical criteria for MNGIE.
  
  
  RESULTS
  Twenty-five of the 180 patients fulfilled the clinical criteria for MNGIE and had homozygous or compound heterozygous TP mutations. All had drastically decreased TP activity [mean (SD), 10 (15) nmol thymine formed. h(-1). (mg protein)(-1) vs 634 (217) nmol thymine formed. h(-1). (mg protein)(-1) for the controls]. Relative to the control mean, TP activities were reduced to 35% in mutation carriers and 65% in MNGIE-like patients. All 25 MNGIE patients had detectable plasma dThd [8.6 (3.4) micromol/L] and dUrd [14.2 (4.4) micromol/L]. Controls, carriers, and MNGIE-like patients showed no detectable plasma dThd and dUrd.
  
  
  CONCLUSIONS
  We propose a diagnostic algorithm based on the determination of plasma dThd and dUrd, TP activity in buffy coat, or both to make a definitive diagnosis of MNGIE. Increased concentrations of dThd (>3 micromol/L) and dUrd (>5 micromol/L) in plasma or a decrease in buffy coat TP activity to </=8% relative to controls is sufficient to diagnose MNGIE.
authors.affiliation: Department of Neurology, Columbia University College of Physicians and Surgeons, New York, NY, USA.
authors.forename: Ramon
authors.initials: R
authors.lastname: Martí
authors.forename: Antonella
authors.initials: A
authors.lastname: Spinazzola
authors.forename: Saba
authors.initials: S
authors.lastname: Tadesse
authors.forename: Ichizo
authors.initials: I
authors.lastname: Nishino
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Nishigaki
authors.forename: Michio
authors.initials: M
authors.lastname: Hirano
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003857:Deoxyuridine / Q000097:blood; D005767:Gastrointestinal Diseases / Q000175:diagnosis*; D006801:Humans; D017237:Mitochondrial Encephalomyopathies / Q000175:diagnosis*; D009154:Mutation; D013936:Thymidine / Q000097:blood; D013939:Thymidine Phosphorylase / Q000097:blood / Q000235:genetics
chemical_list: D013939:Thymidine Phosphorylase; D013936:Thymidine; D003857:Deoxyuridine