RELATIONSHIP OF ELEVATED BLOOD TYROSINE TO THE ULTIMATE INTELLECTUAL PERFORMANCE OF PREMATURE INFANTS

Abstract

Blood tyrosine concentrations were followed from birth to nursery discharge in 71 premature infants fed a high protein formula supplemented by 60 mg/day of ascorbic acid. In 89% of infants blood tyrosine concentrations were abnormal, and in 38% of infants the maximum level observed was 15.0 mg/100 ml or higher. Maximum blood tyrosine levels correlated significantly with gestational age (p = < 0.05) but not with birth weight. In a follow-up study performed at 15 months of age, infants with high tyrosine levels had no increase in the incidence of neurological abnormalities. Between 7 and 8 years of age a second follow-up study was performed on 62 children. This included a WISC, a Wide-Range Achievement Test (WRAT), and tests for psychomotor and language maturity. Two children had died in the interval, and five of the 62 were retarded for full testing. The full scale WISC I.Q. of all children correlated with birth weight at the 10% confidence level (p = < 0.1). The mean WISC I.Q. of high and low tyrosine subjects was 82.9 and 81.6 respectively. When infants were grouped by birth weight, a significant difference was detected in subjects weighing 2,000 gm or more. High tyrosine infants had a significantly lower performance I.Q. than low tyrosine infants (82.4 and 97.8 respectively; p = < 0.02). Significant differences were recorded in the scores on Object Assembly, Picture Assembly, and Picture Completion of the WISC. Significant differences were also seen on the Spelling subtest of the WRAT (p = < 0.02). We observed no adverse effect of high tyrosine levels on the intellectual performance of smaller premature infants, who on the whole have a greater risk for other complications of prematurity.