NONACIDOTIC KIDNEY PROXIMAL TUBULOPATHY WITH ABSORPTIVE HYPERCALCIURIA

We studied three patients with proximal tubulopathy characterized by d efective reabsorption of phosphate, glucose, amino acids, urate, and l ow molecular weight proteins. This tubulopathy differs from Fanconi sy ndrome in that the patients had normal plasma bicarbonate and absorpti ve hypercalciuria associated with increased 1,25-dihydroxyvitamin D le vels. The youngest patient was rachitic and may be classified with pre viously described patients, whereas the other two patients presented w ith nonrachitic osteopenic bone disease and their tubulopathy started during adult life, Kidney defects appeared sequentially in one of the nonrachitic patients. The two brothers of the youngest patient had sim ilar kidney and bone disturbances. One of the other two patients had a brother with similar kidney reabsorption defects; an additional broth er was probably affected and a sister presented with glycosuria, but n o other reabsorption defects. The findings in these two families sugge st a genetic transmission of proximal tubulopathy. The third case was sporadic. Renal histology of the three patients showed a great number of giant cells in the tubular lumen. We conclude that, at least in our adult patients, tubulopathy may represent a new entity among the prox imal tubular dysfunction cases described to date. The features of this proximal defect suggest that it may be caused by a selective alterati on of luminal cell membrane transport of phosphate, glucose, amino aci ds, urate, and proteins in the presence of a normal sodium gradient ac ross the tubular cell membrane. (C) 1995 by the National Kidney Founda tion, Inc.