INCREASED URINARY ALBUMIN ANDRETINOL-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 wh ether 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 inherite d. RESEARCH DESIGN AND METHODS - We estimated both urinary albumin exc retion (UAE) and urinary retinol-binding protein (RBP) in 51 identical twin pairs discordant for type I dibetes and in 51 matched control su bjects. RESULTS - UAE and RBP were significantly higher in the diabeti c 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 mu g/min), diabetic twins had both a highe r 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] mu g/mmol cre atinine) 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 re sults suggest that in type I diabetes, an index of renal tubular funct ion (RBP), but not glomerular function (UAE), is influenced by shared genetic and non-genetic factors. Type I diabetes can affect renal tubu lar 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.