The genome and the environment act in concert to determine all of an individual’s characteristics. A classical pathological example of a gene-environment interaction is phenylketonuria, in which dietary phenylalanine causes severe mental retardation in individuals harboring mutations in the tyrosine hydroxylase gene.37 In this case, elimination of phenylalanine from the diet is preventative. For common conditions such as diabetes and coronary disease, a wealth of epidemiological data show that environmental factors accelerate disease, sometimes with influence spanning generations.38,39 Broadly, external interactions with the genome affecting the expression of traits is known as epigenomics.
