Tyrosinemia and Tyrosinuria in Low-Birth-Weight Infants

Abstract

Blood levels and urinary excretion of tyrosine were determined in 31 low-birth\x=req-\ weight infants. Fourteen of these infants were preterm and 17 were born at term. Gestational age was assessed by menstrual history, and doubtful cases were corrected by neurological examination. Both plasma and urinary tyrosine levels were markedly increased in infants whose gestational age was below 38 weeks. These differences were present regardless of the infant's birth weight. Thus, the changing pattern of tyrosine metabolism, previously described, is a phenomenon associated with maturity and not with birth weight. These data supply a practical biochemical method for assessing gestational age in low-birth-weight infants. Some years ago the classical studies of Levine and his group'"' showed that premature infants be¬ low 2,200 gm (4 lb 14 oz), fed with high-protein formulas, excreted large amounts of tyrosine and its deriva¬ tives in their urine. It was also ob¬ served3 that the excretion of p-hydroxyphenylpyruvic acid ranged be¬ tween 223 and 698 mg/24 hr. This high urinary excretion was main¬ tained when the diet was not supple-