Epigenetics, or Why the Question isn't "Environment OR Genetics"

The study of genetics has been all the rage recently in medical science.  While it has led to some groundbreaking developments in the treatment of disease as well as even how we conceive of the concept of disease, it has been emphasized as the PRIMARY factor in so many cases in a way reminiscent of the saying "when holding a hammer, everything looks like a nail".  Most people seem to understand the idea of a genetic cause for illness, or even a genetic role in disease, as meaning that we are helpless to do anything to treat or prevent the illness; that all we can do is throw up our hands and admit powerlessness.  More than anything, autism is the example of this kind of thinking as well as the example that shows the fallacy of this viewpoint. 

This is largely due to the fact that most people have an outdated and very incomplete idea of what the term "genetic" means.  In high school biology class I was taught that our DNA hold the instructions for making us, encoded in a series of nucleotides (As, Ts, Gs, and Cs).  Our "genetic code" is seen as a kind if instruction book that says "make this person this tall, with this color hair and eyes, and with this personality".  It is seen by many as something that is "used" in the beginning, when we are growing as a fetus, and that results in unchangeable characteristics in us.  This is actually quite far from the truth.  An excellent article about epigenetics and how they relate to our behavior and health was recently published in the magazine Discover, which is a great place to start in understanding this perspective.  You can also watch a narrated slide show from the science show NOVA about epigenetics here...another level or aspect of our genetics that is keenly responsive to our environment: 

This is a quote from the webpage with the link to the slideshow "In this audio slide show, Dr. Dana Dolinoy of Duke University explains the role that the epigenome, a sort of second genome, plays in regulating the expression of our genes. As Dolinoy notes, we can no longer say with certainty whether genetics or the environment have a greater impact on our health, because the two are inextricably linked through the epigenome."  Let me emphasize that last part..."we can no longer say with certainty whether genetics or the environment have a greater impact on our health, because the two are inextricably linked through the epigenome."   The question that dominates media coverage of autism- the question of "whether the cause is genetic OR environmental" is moot.  It is both, both are inter-related.  There is another famous quote (please post in the comments if you remember who said it, I don't) is "genetics is stored environment". 

The "reading" of your genetic code is not a passive process but an active process that is influenced by your environment, it is regulated by proteins that control which genes are turned on and when, in which part of the development process, and for how long. Many toxins in the environment including metals, pesticides, and chemical additives are known to effect this process, as are infections, nutritional factors, and even social factors. This quote from the journal article Prenatal environmental exposures, epigenetics, and disease explains this very well:

"Epigenetics is the study of heritable changes in gene expression or phenotype occurring without changes in DNA sequence. The genetic information in DNA has been likened to the notes of an orchestral score and epigenetics to the conductor who interprets the score and controls the dynamics of the symphonic performance. While new epigenetic mechanisms are being uncovered, the best characterized are DNA methylation, changes in histone proteins around which DNA is packaged, and expression of non-coding RNAs. Interactions between these epigenetic mechanisms generate diversity of cell types during development and then maintain the expression profiles of the different cell types throughout life. The term “environmental epigenomics” reflects the constant interplay between the environment, which includes both endogenous (such as hormone levels or immune status) and exogenous factors (such as nutritional and chemical exposures), and the epigenome. The best characterized epigenetic events in early mammalian development are genomic imprinting (the silencing of one parental allele at a single locus, which occurs in the parental germ stem cells) resulting in monoallelic gene expression and x-chromosome inactivation (silencing of one of the two X chromosomes in mammalian females) occurring in early embryogenesis. Dysregulation of imprinted genes during early development is involved in disorders such as Angelman’s, Prader-Willi and Beckwith-Wiederman Syndromes, certain cancers, and possibly in autism and other neurological syndromes."

For more on the basics of epigenetics: 

Epigenetics and the influence of our genes this is a TED talk that is both thorough and dense but very helpful.

There is an episode of the tv show NOVA called "Ghost in Your Genes" that provides a good introduction to how epigenetics works.

The Power Of Genes, And The Line Between Biology And Destiny from NPR

The illustrated guide to epigenetics (from the magazine Mother Jones)

For very detailed and advanced information about epigenetics this lecture by Dr. Laura Landweber is very good "Epigenetics: Rewriting the information in DNA".

Also Science 101 for Parents: How Epigenetics is Revolutionizing the Understanding of Heredity which is a lecture presented at Rockefeller University that also gets into more advanced topics and also is more focused on the role of epigenetics in child development.