title: The 5'VNTR proinsulin gene (INS) polymorphism and the functional reserve of β cells in the intravenous glucose tolerance test.
abstract: BACKGROUND
  Proinsulin 5'VNTR polymorphism determines susceptibility to type 1 diabetes (T1DM). The authors tested whether it affects intravenous glucose tolerance test (IVGTT) results.
  
  
  OBJECTIVE
  To evaluate a possible relationship between 5'VNTR proinsulin gene (INS) polymorphism and glucose, insulin and C-peptide levels during IVGTT among siblings of children suffering from T1DM.
  
  
  METHODS
  Fourteen patients - siblings of children with type 1 diabetes, positive for at least one autoantibody, underwent IVGTT with glucose, insulin and C-peptide concentrations measurement.
  
  
  RESULTS
  Mean age of patients equaled 10.71 ± 4.15 years. Eight individuals were homozygous for class I/I and six were class III/I heterozygotes. No significant differences in blood glucose levels during the IVGTT were observed (p=0.67). However, lower insulin (p=0.03) and C-peptide (p=0.01) levels were observed in I/I homozygotes in post-challenge timepoints. No significant differences were observed in baseline fasting insulin, glucose and C-peptide levels.
  
  
  CONCLUSIONS
  The class III allele in the 5'VNTR promoter region of INS is associated with a greater functional reserve of β cells in response to a direct hyperglycemic stimulus in individuals with a familial background of T1DM.
authors.affiliation: Department of Pediatrics, Medical University of Lodz, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Fendler
authors.forename: Krystyna
authors.initials: K
authors.lastname: Wyka
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Cieślik-Heinrich
authors.forename: Ewa
authors.initials: E
authors.lastname: Polakowska
authors.forename: Justyna
authors.initials: J
authors.lastname: Jastrzębska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Młynarski
mesh_terms: D000293:Adolescent; D001786:Blood Glucose / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000235:genetics*; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000235:genetics; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D018598:Minisatellite Repeats / Q000235:genetics; D011110:Polymorphism, Genetic; D011384:Proinsulin / Q000235:genetics*; D012016:Reference Values; D035781:Siblings
chemical_list: D001786:Blood Glucose; D007328:Insulin; D011384:Proinsulin