Early effect of NTBC on renal tubular dysfunction in hereditary tyrosinemia type 1.

Background: Hereditary tyrosinemia type 1 (HT1) is characterized by severe progressive liver disease and renal tubular dysfunction. NTBC therapy has revolutionized the management of HT1 but its effect on renal tubular function has so far been poorly investigated. The aim of this study was to describe the early effect of NTBC on renal tubular disease in patients with HT1.

Methods: Five HT1 patients (age between 5 and 53 months) with different types of presentation were evaluated before and during the first 2 weeks of therapy with NTBC in a retrospective case analysis for phosphate metabolism and renal tubular function.

Results: Before starting NTBC therapy, all children manifested signs of renal dysfunction which included hypophosphatemia, acidosis, reduced phosphate reabsorption, aminoaciduria, glycosuria (Fanconi syndrome), and variable degree of proteinuria. Some patients also presented increased urinary calcium/creatinine ratio and raised fractional excretion of sodium. Starting of NTBC therapy resulted in the rapid normalization of plasma phosphate within one week from its initiation in majority of patients and in all patients during the second week of therapy. TmP/GFR normalized in 48h, while the other markers of renal dysfunction showed an improving trend over 2 weeks.

Conclusions: NTBC is an efficient treatment for renal tubular dysfunction in HT1, allowing the return to normal function within a few weeks. Its early effect on renal tubular cells appeared to be very rapid, particularly in normalizing plasma phosphate and TmP/GFR. In our series of patients, the TmP/GFR resulted as the most reliable index of tubular function.