In today’s modern age, with the entire human genetic makeup (the genome) decoded and genetic testing more and more common, most people understand that changes, or mutations, in genes can lead to death, disease, and disorder. But there is another way our genes play a role in physical dysfunction, and that occurs without direct alterations to DNA, the substance that makes up genes. Increasingly, researchers and physicians are exploring the concept of “epigenetics”— those changes that influence how genes are expressed but which do not involve physical changes in the DNA itself.

http://pubs.niaaa.nih.gov/publications/aa86/aa86.htm