Did you happen to see this article in the New York Times: Why Fathers Really Matter. This article introduces the concept of epigenetics. Epigenetics can be defined as “the set of modifications to our genetic material that change the way genes are switched on or off, but which don’t alter the genes themselves.” ¹ Epigenetics helps to explain the relationship between a person’s genotype (the genetic makeup as defined by DNA) and phenotype (physical appearance and traits). The classic example of this is identical twins. Identical twins have identical genotypes but different phenotypes. Their differences become more apparent as they age, because the environment plays an important role in epigenetic modifications. Research in this field is exploding, because herein lies a key to the relationship between an individual’s genetic code, the environment, aging and disease.
It is now known that epigenetic modifications or marks consist of chemical groups that are stuck onto DNA without changing the DNA. They sit on top of the genetic code and control the activation and deactivation of genes. This explains why neurons are so different from skin cells, even though they all contain the same genetic code. If skin cells divide, they become new skin cells. All the genes are deactivated except for the ones needed for the skin cells to look and behave like skin cells.
But epigenetic modification can also be very fluid. These chemical switches on DNA govern protein production—which ones will be produced, when, for how long, how much, etc.
- Think enzymes that control metabolic processes and their impact on health.
- Think hormones and their profound influence on child development.
- Think neurotransmitters that impact learning and the growth of synapses.
In the New York Times article, the author, Judith Shulevitz, describes why she has become obsessed with epigenetics: “because it strikes me as both game-changing and terrifying.” Here are two reasons why:
- Epigenetic mechanisms of gene expression and suppression are influenced by the environment. Our phenotype is not written in the stone of our DNA. Physical traits, mental status, and the development of disease can be shaped by environmental factors such as the food we eat, the air we breathe, our exposure to traumatic events, and our age.
- Epigenetic modifications are heritable. A recent journal article cited over 100 examples of epigenetic inheritance, in both animals and humans.
One of the best known example of both of these principles of epigenetics in humans is an epidemiological study of the people living through the “Dutch Hunger Winter” of 1944-45, during which over 20,000 people died of starvation. Scientists were able to evaluate the long-term effects of the famine among the survivors, including pregnant women and their children. If a woman was well nourished during the first portion of her pregnancy but malnourished for the last few months, her baby was likely to have a lower birth weight. On the other hand, if the baby was conceived towards the end of the famine and the mother was malnourished only during the first trimester, she was likely to have a normal birth weight baby. This is not surprising, because babies do most of their growing during the last months of a pregnancy. But long-term effects were very surprising. The babies that were born small stayed small for the rest of their lives, with lower obesity rates than the general population (Audrey Hepburn was one of these babies). The normal birth weight babies who were poorly nourished during the first trimester were more likely to become obese as adults. A major environmental event (the famine) changed the epigenetic programming of the developing fetus. The epigenetic modifications of the babies that were malnourished during the first trimester enabled them to survive by making the most of a bad situation. But this reprogramming remained in effect long after the famine that caused it. It is thought that epigenetic modifications to the genes regulating metabolism resulted in a greater likelihood of becoming obese. Even more extraordinary was the presence of these effects in future generations. The grandchildren were more likely to be skinny or obese. Something that happened to a population of pregnant women affected their children and their children’s children!
While Shulevitz has chosen to describe epigenetics as “game-changing and terrifying,” others view epigenetics as the new frontier in fighting disease. Epigenetic therapies are already being used to fight various cancers. The role of epigenetics in depression, autism, Alzheimer’s disease and addiction are being explored. An understanding of epigenetics may prepare us to face the global obesity epidemic. The epigenetics revolution is underway, and the implications for patient care today and tomorrow are profound.
1. Carey N. The Epigenetics Revolution: How Modern Biology is Rewriting Our Understanding of Genetics, Disease and Inheritance. Columbia University Press: 2012.
[i] Carey N. The Epigenetics Revolution. 2012