title: Increased urinary albumin and retinol-binding protein in type I diabetes. A study of identical twins.
abstract: OBJECTIVE
  Indexes of early renal glomerular and tubular dysfunction have been demonstrated in type I diabetes, but it remains uncertain whether such changes are genetically determined or are secondary to the disease process. We therefore undertook to study whether early markers of renal dysfunction are a consequence of type I diabetes or inherited.
  
  
  METHODS
  We estimated both urinary albumin excretion (UAE) and urinary retinol-binding protein (RBP) in 51 identical twin pairs discordant for type I diabetes and in 51 matched control subjects.
  
  
  RESULTS
  UAE and RBP were significantly higher in the diabetic twins than in their nondiabetic co-twins (P < 0.0001 and P < 0.0002, respectively). Seven diabetic twins had elevated UAE, but none of the nondiabetic co-twins did. In a subgroup of 44 twins with normal UAE (albumin excretion rate < 20 micrograms/min), diabetic twins had both a higher albumin excretion function (median [range]; 0.64 [0.18-2.74] mg/mmol creatinine) than their nondiabetic co-twins (0.48 [0.24-1.40], P < 0.01) and higher levels of RBP excretion (10.4 [4.0-167.0] micrograms/mmol creatinine) than their nondiabetic co-twins (7.5 [0.97-23.0], P < 0.05). Values between twins of a pair were significantly correlated for RBP (r = 0.36, P < 0.05) but not for UAE (r = 0.13).
  
  
  CONCLUSIONS
  These results suggest that in type I diabetes, an index of renal tubular function (RBP), but not glomerular function (UAE), is influenced by shared genetic and nongenetic factors. Type I diabetes can affect renal tubular function even when glomerular function is normal. We conclude that neither the increased UAE nor urinary RBP found in type I diabetes is inherited independently of the diabetes process.
authors.affiliation: Academic Unit of Cardiovascular Medicine, Charing Cross Hospital, London, U.K.
authors.forename: S W
authors.initials: SW
authors.lastname: Dubrey
authors.forename: R
authors.initials: R
authors.lastname: Beetham
authors.forename: J
authors.initials: J
authors.lastname: Miles
authors.forename: M I
authors.initials: MI
authors.lastname: Noble
authors.forename: R
authors.initials: R
authors.lastname: Rowe
authors.forename: R D
authors.initials: RD
authors.lastname: Leslie
mesh_terms: D000328:Adult; D000419:Albuminuria / Q000652:urine*; D015331:Cohort Studies; D003922:Diabetes Mellitus, Type 1 / Q000503:physiopathology / Q000652:urine*; D004200:Diseases in Twins; D005260:Female; D006801:Humans; D007678:Kidney Glomerulus / Q000503:physiopathology*; D007684:Kidney Tubules / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012177:Retinol-Binding Proteins / Q000652:urine*; D014430:Twins, Monozygotic
chemical_list: D012177:Retinol-Binding Proteins