Phenylketonuria in Children and Mothers: Genes, Environments, Behavior.

Phenylketonuria (PKU) is an inborn metabolic error in which metabolism of phenylalanine into tyrosine is disrupted. If the diet of an infant with PKU is not restricted, blood phenylalanine levels are elevated, leading to irremediable brain damage and severe mental retardation. Children with PKU who are placed early and continuously on a low-phenylalanine diet develop normal levels of intelligence, and brain damage is largely prevented. However, if the diet of a mother with PKU is unrestricted during her pregnancy, high phenylalanine levels in her blood can cross the placental barrier and damage the developing fetus in multiple ways. These results demonstrate how genes and environmental factors combine to create prenatal environments that can have profound effects on the growth and development of offspring during infancy and childhood.