The development of infant monkeys fed low phenylalanine diets.

Abstract

Extract: The nutritional adequacy of a commercial low-phenylalanine diet (Diet LF) has been investigated in infant rhesus monkeys. All animals were fed a control diet (Diet CD) during the first month of life. Thereafter, animals in Group A were fed LF until seventy-five days of age. This diet was then supplemented with 0.1 g of L-phenylalanine per kilogram of body weight until 105 days of age and with 0.2 g of L-phenylalanine per kilogram from 105 to 135 days of age. Animals in Group B were fed LF supplemented with an amount of L-phenylalanine equal to that contained in CD (0.087 g/100 ml) from 30 to 135 days of age. For the remainder of the first year of life, all animals were again fed CD. Animals in Group A developed growth failure, anemia, hypoproteinemia, dermatitis, edema, hypophenylalaninemia and elevated levels of several other free amino acids in serum when fed LF. The addition of supplements of L-phenylalanine corrected hypoproteinemia, hypophenylalaninemia, and anemia, but improvement of dermatitis and growth rates were not seen until the animals were again fed CD. Animals in Group B developed dermatitis and elevated levels of several of the free amino acids in serum, but showed no other biochemical or clinical evidence of phenylalanine deficiency. After one year of age, all animals were evaluated for learning behavior. There was a significant decrease in the learning ability of animals in Group A, while that of animals in Group B was comparable with that of control animals. Speculation: Synthetic diets have been proposed as specific therapy for those inborn errors of metabolism that usually result in serious disability or death. Infant rhesus monkeys fed a commercial low-phenylalanine diet developed a syndrome of phenylalanine deficiency comparable with that which has been reported in some human infants fed the same diet. This study demonstrates the potential adverse effects of any diet deficient in essential nutrients and indicates that this subhuman primate may be of value in investigating the nutritional adequacy of other synthetic diets that may be proposed for use in children.