Studies on Tyrosinosis: 1, Effect of Low-tyrosine and Low-phenylalanine Diet

Abstract

A case of tyrosinosis in a 2-year-old girl is described in which the serum-tyrosine level was raised and the urinary excretion of p-hydroxy-phenyl-pynivic acid, p-hydroxyphenyl-lactic acid, and p-hydroxyphenyl-acetic acid increased greatly. There was marked hyperphosphaturia and hyperaminoaciduria. A 4-weeks trial with a low-tyrosine and low-phenylalanine diet decreased the serum-tyrosine level and increased the serum P. The excretion of the tyrosine metabolites, amino-acids, and P in the urine decreased, as did the excretion of renal epithelial cells and renal casts. On adding L-tyrosine to the low-tyrosine and low-phenylalanine diet the serum tyrosine again increased and the serum P decreased. There was an increase in the urinary excretion of the tyrosine metabolites, amino-acids, and P. These findings support the hypothesis that tyrosinosis is caused by a defect of p-hydroxyphenyl-pyruvate oxidase, and indicate that tyrosine or its metabolites have a "toxic" effect on renal tubular cells and possibly on liver cells.