[Familial proximal tubular azotemia. Elevated urea plasma levels in normal kidney function]

A family showed a renal disturbance, characterized by an elevated urea plasma concentration while glomerular filtration was found to be normal. A detailed study of renal clearance was performed on two members of this family in order to define the nature and site of the disorder. Evidence points to an isolated impairment of urea elimination, giving rise to a reduced urea concentrating ability and thus to a decrease in maximum urine concentration and water conservation. The most probable site of this impairment seems to be the proximal tubule.