Increased urinary albumin and retinol-binding protein in type I diabetes. A study of identical twins.
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.
Dubrey
S W
SW
Academic Unit of Cardiovascular Medicine, Charing Cross Hospital, London, U.K.
Beetham
R
R
Miles
J
J
Noble
M I
MI
Rowe
R
R
Leslie
R D
RD
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
D012177:Retinol-Binding Proteins