 Physically, the somatic epitype corresponds to changes in DNA methylation, oxidative damage (replacement of GTP with oxo-8-dGTP), or changes in DNA-chromatin structure that are not reversed by normal cellular or nuclear repair mechanisms.Somatic epitypes alter gene expression levels without altering the amino acid sequence of the expressed protein.Current research suggests that somatic epitypes can be altered both before and after birth, and this alteration can be in response to exposure to heavy metals (such as lead), differences in maternal care, or nutritional or behavioral stress.