Effect of elevated blood tyrosine on intellectual development of premature infants

Abstract

Blood tyrosines 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% tyrosine concentrations were abnormal, and in 38% the maximum observed was 5.0 mg% or higher. Maximum blood tyrosine correlated with gestational age (p < 0.05) but not with birth weight.On a follow-up study performed at 15 months, infants with high tyrosine levels had no increase in neurological abnormalities. Between 7 and 8 years a second follow-up was done on 64 children. This included a WISC and tests for psychomotor function. Two children had died in the interval and six others were too retarded for full testing. The full scale IQ of all children correlated with birth weight (p < 0.01). The mean IQ of high and low tyrosine subjects was 85.9 and 86.2, respectively. When infants were grouped by birth weight a significant difference was detected in subjects weighing 2000+ gm.Significant differences were recorded in scores on object assembly (p < 0.05), picture assembly (p < 0.05), and picture completion (p < 0.10). We observed no effect of high tyrosine levels on intellectual performance of smaller infants, who, on the whole, are a greater risk for other complications of prematurity.