Renal hypertrophy is the primary dysfunction that leads to diabetic nephropathy, findings suggest
RENAL HYPERTROPHY is a major factor in the development of diabetic nephropathy in patients with type 1 diabetes.
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Gianpaolo Zerbini, MD, of the Istituto Scientifico San Raffaele in Milan, and his colleagues studied 146 patients with type 1 diabetes and normal renal function. They determined baseline kidney volume and glomerular filtration rate (GFR). These patients were compared with a control group of 30 nondiabetics.
After a mean follow-up of 8.1 years, microalbuminuria developed in 27 patients (18.5%), the investigators reported in Diabetes (2006;55:2620-2625). The mean albumin excretion rate rose from 7.9 to 110.4 µg/min. In the other 119 patients, the mean albumin excretion rate remained with-in the normal range (from 6.3 to 7.4 µg/min) after a mean follow-up of 9.8 years (normoalbuminuria group).
At baseline, kidney volume was higher in the diabetics than the controls (287.2 vs. 236.8 mL/1.73 m2). The microalbuminuria group had significantly higher kidney volumes than the normoalbuminuria group and controls (312.8 vs. 281.4 vs. 236.8 mL/1.73 m2, respectively). In the diabetes patients, microalbuminuria developed in 15 of 110 patients (13.6%) with normal kidney volume and 12 of 36 patients (33.3%) with type 1 diabetes and increased kidney volume.
Baseline GFR in the microalbuminuria group was similar to that of the normoalbuminuria group (121.7 and 117.6 mL/min per 1.73 m2, respectively), but higher than the GFR in the controls (110.7 mL/min per 1.73 m2), the study found.
The researchers also examined a subset of 68 patients who underwent a second evaluation of kidney volume and GFR four years after the baseline evaluation. This analysis also showed that the risk of progression to microalbuminuria was significantly higher in patients with a greater increase in kidney volume. During the four years, kidney volume increased to a greater extent in the microalbuminuria group (from 311.0 to 328.2 mL/1.73 m2) than in the normoalbuminuria group (279.7 to 283.0 mL/1.73 m2). GFR decreased significantly in both groups, but the decline was greater in the microalbuminuria group (from 126.1 to 102.9 mL/min per 1.73 m2 vs. a decline from 124.4 to 115.3 mL/min per 1.73 m2 in the normoalbuminuria subjects).
The investigators concluded that their findings “support the hypothesis that renal hypertrophy is the primary dysfunction in the development of diabetic nephropathy.
