For many years scientists tried to understand how a fertilized egg develops into a multicellular organism with specialized cells. Even though cells in our body share the same set of genes, some cells have “learned” how to perform special functions. Our muscle cells somehow fill themselves with muscle proteins called myosin and actin that let them contract; skin cells manage to make keratin, a protein that repels water and resists abrasion; and retina cells form pigments capable of absorbing light rays.

In 1942, the embryologist Conrad Waddington coined the term “epigenetics” where “epi” means “above” or “in addition to.” His creation of the term led to a new field of study. Epigenetics addresses the question of how specialized cells work and also explores traits that we inherit from generations before us.

How exactly is epigenetics “above” genetics? We have all kinds of genetic information encoded in our genome. But only bits and pieces are used in individual cells. Epigenetics is responsible for “cherry picking” what information is used, when and where. This concept is more fully explained in the Central Dogma of molecular biology, a theory that states that genetic material moves in one direction only. DNA is transcribed into RNA, which then forms a protein from a single expressed gene.

For example, a fertilized egg contains genes that have the instructions necessary to form each cell in our body. However, during development, as a particular cell commits to a specific path, sometimes it “turns off” certain genes. Most genes in a cell that is destined to become a skin cell, for instance, will silence themselves to allow this growing cell to fill itself with keratin. But if the wrong genes continue to express in a cell that should have switched off and become silent, disease will develop.      

Interestingly, epigenetic studies have found that our health may be influenced by the lifestyle, diet and environmental stress that our parents and grandparents were exposed to during their lives. Epigenetic studies suggest that people are most sensitive to environmental challenges during fetal development, early childhood and adolescence. These challenges may have affected the quality of our parents’ and grandparents’ sperm and eggs, which in turn can affect our own development. This phenomenon, called transgenerational inheritance, explores this link.

One example of transgenerational inheritance is a study that was conducted in Sweden. Researchers found that the sons and grandsons of people defined as being at a “social disadvantage” (i.e., were raised by single mothers) in the early 20th century had a significant risk of developing circulatory disease compared to descendants of people who were raised by both parents. 

As we learn more about epigenetic mechanisms and their role in human disease, the progress toward new treatments, including lifestyle interventions and personalized precision medicine, will help to extend our life- and healthspan.