Epigenetics: beyond our genes

If the genetic information contained in the DNA is faithfully transmitted from one cell to another at each division, how do you explain the differences between twins? Have you ever wondered why a neuron looks nothing like a skin cell if they share the same DNA?

These questions cannot be answered with the principles of classical genetics based on genes, since the twins come from the same zygote, a cell that divided into identical daughter cells with the same genetic material and that, eventually, gave rise to two independent individuals that we could not consider identical. The same happens in the case of the different cell types in our body, but what is behind these differences?

Epigenetics is the answer to these questions.

If you continue reading this article, you will discover:

  • What epigenetics is
  • What relationship has with the appearance of pathologies in the skin

What is epigenetics?

The term epigenetics was coined by Conrad H. Waddington in the early 1940s and is defined as the study of changes in gene function that are unrelated to their DNA sequence.

Within each of our cells, the DNA is associated with proteins, called histones, that allow to achieve an ordered structure. Depending on the packaging level, the DNA can be found as chromatin or forming higher structures such as chromosomes.

Image from National Human Genome Research Institute

There are epigenetic mechanisms that consist of chemical modifications, such as histone acetylation and DNA methylation, that determine the expression of different genes in cells with the same genetic material. Depending on the modifications in each gene, the cellular machinery responsible for expressing them will or will not join the DNA to start the process of gene transcription and translation.

In other words, if our genetic information was a novel, epigenetics would be in charge of turning the corner of the pages that we should read, and we would only read those. Finally, depending on the parts we had read, we could summarize the story differently from someone who had read others.

Epigenetics, environment, and skin.

As we described in a previous article, there are two types of factors that affect the state of our skin: endogenous and exogenous. Epigenetics may proof that there is a relationship between them, so that certain environmental factors can modify the expression of genes in cells of our body and, therefore, our skin.

Some of the external factors to which we are exposed throughout our lives are: lifestyle, tobacco, alcohol, diet, and exposure to different physical, chemical and/or biological factors.

Recent data indicate that the epigenetic modifications that we find in a healthy individual differ from those of people with atopic dermatitis. These variations affect genes important for the differentiation and proliferation of skin cells, as well as genes related to the immune response in the affected epidermis of patients with dermatitis.

Epigenetic epidemiology and the hygiene hypothesis.

Epigenetic epidemiology is defined as the study of the association between epigenetic variations and the existing risk of developing a disease.

Beyond the exogenous factors described above, the hygiene hypothesis suggests that exposure to repeated infections in the first years of life leads to a lower incidence of immune-mediated hypersensitivity diseases, such as atopic dermatitis.

This hypothesis is based on the fact that the prevalence of this type of pathology increased at the same time as the implementation of a greater number of hygiene measures after the industrial revolution.

We no longer talk only about infections as such, but about all the microorganisms with which we come into contact from, even, the day of our birth: the way of feeding during the first months of life (breast milk or bottle), the type of birth (vaginal delivery or caesarean section) and exposure to antibiotics can cause variations in our microbiota and become risk factors in the development of inflammatory diseases.

These variations in the prevalence of immunological diseases cannot be explained only by genetic factors, but gene-environment interaction, that is, epigenetics, must be included in order to arrive at a convincing explanation.

Thus, the information provided by epigenetic epidemiology could be used for preventive treatments, early diagnoses and treatments during the disease. Furthermore, as epigenetic epidemiology evaluates the relationship between epigenetic alterations and the risk of developing the disease for each individual, it is directly related to the development of personalized medicine.

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Nedoszytko B, Reszka E, Gutowska-Owsiak D, Trzeciak M, Lange M, Jarczak J, … Kalinowski L. Genetic and Epigenetic Aspects of Atopic Dermatitis. Int J Mol Sci. 2020; 21(18): 6484

Bae JM. Interpretation of the hygiene and microflora hypothesis for allergic diseases through epigenetic epidemiology. Epidemiol Health. 2018; 40:e2018006

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