What are genes?
DNA is found in the nucleus of each cell in the body. A DNA sequence is made up of 4 different units, also known as nucleotides. These units are Guanine (G), Cytosine (C), Adenine (A) and Thymine (T). The entire DNA sequence for a human is roughly 3 billion of these units which are split across different chromosomes. Strands of DNA wrap around histone proteins to form a nucleosome which allows DNA to form the compact shape of a chromosome. Histones also control the activity of a gene.
A gene is a section of DNA which is arranged in a specific location on a chromosome. Each gene contains information for making a specific protein which is responsible for an individual function or characteristic. Each DNA sequence for every gene is inherited from our parents.
What are epigenetics?
Epigenetics are methods used by the body to regulate which proteins should be made and how many. It can also be used to change how a DNA strand is organised within a cell. In other words, epigenetics alter the expression of a certain gene by changing how your body uses a DNA sequence but does not change the DNA sequence itself. This can be done by adding certain types of chemical tags onto the DNA. Chemical tags can also be added to histone proteins, altering how DNA wraps around it. This influences how a gene is used.
These epigenetic modifications are essential for normal development and cell specialisation. It enables each cell in the body to contain the same genetic information, but produce a unique combination of proteins and other molecules to have a specific structure and function. For example, a brain cell and a skin cell from the same person should have identical DNA but, due to epigenetics, look and behave differently. The chemical tags present at any one time are referred to as the epigenome.
Epigenetics can also be influenced by individual behaviours and the environment. This means personal experiences could influence the chemical tags placed on DNA and histones. Rather than the genes themselves changing (genetic change), experiences may alter how the gene functions (epigenetic change). Epigenetic changes can be permanent or temporary.
How does this relate to mental health?
Until fairly recently, not much was known about the impacts of epigenetics on the brain. This lead to misleading conclusions on the extent of how experiences and environments can impact brain development and function. The regulation of epigenetics is essential for normal brain function. Irregular epigenetic markers can be associated with developmental issues and mental impairment. Many neurological and psychiatric disorders involve epigenetic alterations across multiple genes.
Epigenetics are linked to a range of mental health disorders including depression, anxiety, and schizophrenia. Chronic stress can cause epigenetic modifications in genes which control a stress response. Stress is a widely accepted precursor to some cases of depression, although, the exact process of how it is linked to depression is not well understood. Epigenetic differences are also believed to play a crucial role in addiction as observed in cases of addiction for nicotine, alcohol and methamphetamine in comparison to individuals with no addiction issues. Some theories suggest the long-lasting nature and delayed response to treatments may be related to epigenetic adaptations.
Traumatic experiences from childhood and even before birth can cause negative epigenetic changes which affect physical and mental health as well as learning abilities and behaviours. 'Intergenerational Trauma' is a theory where the impacts of trauma can be epigenetically inherited several generations after prolonged environmental exposure to stress, toxins, addictive substances and obesity promoting diets.
Epigenetic mechanisms can also be positively influenced with counselling interventions including cognitive behavioural therapy, mindfulness, diet and exercise. Positive experiences such as supportive relationships and beneficial opportunities can also reduce the likelihood of negative epigenetic modifications and reverse epigenetic changes which occur as a result of negative experiences.
References
Tsankova, N., Renthal, W., Kumar, A. et al. Epigenetic regulation in psychiatric disorders. Nat Rev Neurosci 8, 355–367 (2007). https://doi.org/10.1038/nrn2132
Monaco, A.P. An epigenetic, transgenerational model of increased mental health disorders in children, adolescents and young adults. Eur J Hum Genet 29, 387–395 (2021). https://doi.org/10.1038/s41431-020-00726-4
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