Tyrosinemia and tyrosyluria in healthy prematures: time courses not vitamin C-dependent

Tyrosyluria and for a part also tyrosinemia were studied in 60 healthy prematures of various birth weights and gestational ages. The first analyses were performed between the 6th and the 14th day after birth. A normal milk diet was given and the protein-intake was between 3 and 4 g/kg. After the first collection of urine half the patients received extra ascorbic acid, 100 mg/kg daily. Urinary analyses of tyrosine and p-hydroxyphenyl metabolites were performed once a week, until the excretion of p-hydroxyphenylpyruvic plus p-hydroxyphenyllactic acids was lower than 5 mmoles per gram creatinine. In 22 out of the 60 prematures (or 37%) a tyrosyluria of more than 5 mmoles/g creatinine and in 19 out of 44 (43%) patients analysed serum tyrosine was higher than 5 mg/100 ml at first analysis. No inverse correlation between tyrosyluria and tyrosinemia on the one hand and birth weight and gestational age on the other hand existed. But in children with a delayed intra-uterine development the incidence of tyrosyluria was higher as prematurity was more pronounced. Ascorbic acid had no effect on the rate of disappearance of tyrosyluria. It was concluded that the addition of extra vitamin C to the diet of prematures is not useful for the normalization of tyrosine metabolism.