Q:  Does an individual's genome affect how often a gene is methylized a certain environment? Does natural genetic makeup, in fact, influence or nurture effects in adult life?

A: Both of these questions raise an interesting point, which is the interplay of genetic variation and epigenetic mechanisms in the context of the environment. There is no doubt that profound connections exist between our genome, our epigenome and the environment. However, many aspects of this sophisticated and exciting circuitry remain to be discovered, in particular as we learn more about epigenetic variation in human populations.

For example, one can imagine a genetic variation in which the cytosine residue within a DNA methylation site is altered to a different residue, which cannot be methylated. Thus, in this case, the substrate for DNA methylation is not available. In another situation, one can imagine that there could be genetic mutations in enzymes involved in creating the epigenetic landscape that affect the activity or regulatory properties of these enzymes, ultimately resulting in a differential response to environmental cues.

In addition, as Dr. Barr alluded to in his lecture, there are direct gene-environment interactions that occur and profoundly affect the response of an organism to its environment. In most cases documented so far, these kinds of interactions do not directly involve epigenetic modifications.