Molybdenum supplementation in phenylketonuria diets: Adequate in early infancy?

Background: Molybdenum concentrations in formulas exceed those in human mil k by far. Infants with phenylketonuria require semisynthetic phenylalanine- restricted diets. Because these diets ate presently supplemented with molyb denum, a study was conducted to determine whether retention and plasma conc entration in the recipients are equivalent to those of healthy boast-fed in fants. Methods: Balance and plasma studies were conducted in healthy breast-fed in fants (n = 17) and in patients with phe nylketonuria (n = 4) at the age of 4 weeks, and the plasma investigations were repeated at the ages of 4 and 1 2 months. The samples were analyzed by atomic absorption spectroscopy (bala nce studies) and high-resolution inductively coupled plasma mass spectromet ry (plasma). Results: Molybdenum intake and retention in all infants with phenylketonuri a were more than 18 times those of breast-fed infants. The plasma concentra tions reflected these differences. A median of 0.04 (mu g/l was assessed in breast-fed infants at 4 weeks and less than 0.02 mu g/l at 4 months of age . Comparative results of infants with phenylketonuria were 2.9 mu g/l and 2 .5 mu g/l, respectively. There were no significant differences between the groups at 12 months of age. Conclusions: The phenylketonuria diets investigated showed excessive retent ion and plasma concentrations of the essential trace element molybdenum in early infancy. In view of these findings, the present practice of molybdenu m fortification should be revised.