Science for presidents

Genetics

Lifestyle's genetic impact

The epigenome is considered one of the most interesting and promising unexplored territories in the biosciences. Epigenetics, understood as the connection between genes and the environment, will enable us to understand, among other things, how lifestyle affects the expression of genes and why genetics do not fully determine our destiny

GONZALO CASINO | JANUARY 31ST, 2011

The reason that identical twins do not have the same diseases
or grow old at the same pace is located in epigenetics

The genetics of the late twentieth century have been surpassed, amended and supplemented by a new discipline. In the light of new biochemical findings regarding the DNA molecule, it has been necessary to form a new field of study called epigenetics, a field which goes beyond the genetics of Mendel, the father of the classical discipline, and even Watson and Crick, the discoverers of the structure of DNA.

Epigenetics has transformed the way we understand genetic inheritance and diseases, from cancer to mental disorders, rescuing the Lamarckian idea that acquired characteristics can be passed on to future generations. Epigenetics is the biological bridge between genes and the environment and promises to explain a variety of inheritable genetic changes that do not depend on the sequence of DNA bases. Why don’t identical twins develop the same diseases? Why was the health of the sheep Dolly not like that of her cloned sisters and she ended up dying prematurely?

Beyond the four letters

The answer to these and other questions are found in epigenetics, which moves beyond DNA’s four-letter language that combines into three-letter words to give names to amino acids and proteins. The DNA sequence is not all powerful: there are a number of epigenetic indicators that determine whether a particular gene (a string of DNA that normally encodes for a protein) is expressed or not, i.e., whether or not it carries out the biological function for which it is responsible.

The DNA molecule, consisting of 3 billion base pairs, is a two-meter long helical fiber packed into the cell’s nucleus by special packing molecules. The entire genetic package consisting of the DNA and associated proteins (mainly histones) is what is called chromatin (chromosomes). And what scientists are now seeing is that the way DNA is packaged determines which genes are activated.

Diseases such as cancer are the result of a series of both genetic and epigenetic changes
All the cells in a person’s body have the same DNA (as also is the case of identical twins), but it is clear that the cells of the body are very different. What is the difference between a skin cell and a neuron if the DNA is identical? The difference is in the package, in all the biochemical changes that make a gene active or not.

The main and best known of these epigenetic factors is the methylation (the addition of a methyl group) of DNA, but there exist others such as acetylation (addition of an acetyl group) or histone methylation. These epigenetic factors do not affect the gene sequence, but rather they make the packaging of the DNA different and, consequently, make it work in a different way.

Green light, red light

Apart from the packaging metaphor, there are others to help visualize epigenetics’ significance. One of the most important is that epigenetic factors can act as the green and red lights of DNA, signals which permit or stop the expression of genes. But even more importantly for individuals seeking to lead a healthier life is that these signals can be modified by lifestyle. And they are passed on to offspring.

At birth, we all inherit a genome and an epigenome. The genome can only be altered by a mutation, while the epigenome is much more dynamic and can be altered by diet, exposure to toxic substances and other factors related to lifestyle. For example, large consumers of alcohol experience a higher proportion of methylation in their genome, and this could relate to many of the diseases they commonly suffer.

Cancer, like many other diseases, is the result of both genetic and epigenetic changes that we are only now beginning to understand. For example, in general, the DNA of tumor cells shows less methylation than healthy cells. Also, scientists have identified several epigenetic markers in various tumor-associated genes that help detect the disease.

The knowledge of the epigenetics of cancer and other diseases is one of the most promising lines of research in biomedicine today. Earlier this decade, a consortium of public and private organizations launched the Human Epigenome Project with the initial goal of identifying, classifying and interpreting the methylation patterns of human genes in major tissues. At the present moment, it has completed a pilot study, but more and more researchers are joining to work on this daunting task of understanding the genetic and epigenetic components (environmental) of diseases, thus improving their detection and treatment.

NOT SO IDENTICAL TWINS
The reason that identical twins do not have the same diseases or grow old at the same pace is located in epigenetics. At birth, identical twins have the same genome (identical genes) and the same epigenome (the same information for the operation of these genes), but over time their epigenomes differentiate. Manel Esteller, director of the Biology and Epigenetics of Cancer research group at the Institute of Biomedical Research of Bellvitge in Barcelona, played a major role in this finding. Esteller explained that the epigenetic differences found in the DNA of 80 pairs of identical twins are due to external factors such as smoking, diet or exercise, but they can also be attributed to epigenetic drift associated with aging.

Subjects of the article