ABSTRACT
It is important to understand in this example that, as a constituent of the foods we eat, phenylalanine represents an environmental factor. An important question then becomes whether or not a PKU individual's behavioral deficits can be changed by altering levels of phenylalanine. The answer is that it can, if the levels are changed during critical developmental periods. Early postnatal detection and intervention through dietary reduction of phenylalanine can dramatically improve the abilities of PKU patients. Therefore, even though PKU individuals differ genetically from non-PKU persons in their ability to metabolize phenylalanine, the behavioral expression of PKU is dependent upon a G x E interaction, namely the existence of the PKU genotype within a high phenylalanine environment.
