Disease has been traditionally understood as an interaction between the environment (e.g., dietary factors, exercise habits) and our genes (e.g., diabetes). Scientists believe that the relationship between these environmental and genetic factors across one’s lifespan greatly contribute to an individual’s susceptibility for developing certain psychiatric conditions.
Genetic research has been particularly beneficial for showing how certain gene variations, or differences in a person’s genetic makeup, can predispose some people to developing certain mental health problems. Schizophrenia and depressive disorders, for example, are associated with genetic variations, which may be passed down from an individual’s parents and make the person more likely to develop these disorders.
Gene sequences that are passed down from parents hold the instructions for making proteins that will carry out a particular function in a cell. These genes can either be turned “on” or “off” by proteins called transcription factors, which govern whether, when and how much of a gene is activated. Two main types of genetic variations can occur in humans that alter the structure of a chromosome and affect gene expression: single nucleotide polymorphisms (SNPs) and structural variations (e.g., insertions, deletions or duplications of small DNA segments). These gene alterations can lead to permanent changes in the DNA sequence, which makes up a gene. Those changes can alter the development of different structures and organs during development and influence the risk for developing certain disorders later in life.
Epigenetic factors: Understanding environmental causes of disease
Epigenetic factors are involved in normal cellular processes and can switch genes on or off and determine which genes are transcribed. Unlike genetics, epigenetic changes can sometimes be triggered by environmental or behavioral circumstances. The study of the processes contributing to inherited changes in the way a gene is expressed — without changing the DNA itself — is called epigenetics. That is, these epigenetic factors can flip the “on-off” switch on genes and change the genetic code of offspring, which may increase an individual’s susceptibility to developing a number of illnesses, behaviors and other health conditions, including respiratory, cardiovascular, reproductive, autoimmune and neurobehavioral conditions.
Epigenetic factors may even be more important than genetics for understanding the environmental causes of disease, said Jean-Pierre Issa, cancer biologist from The University of Texas. Researchers have suggested that environmental factors have a profound influence on the susceptibility for disease. These environmental factors include: diet, stress, lifestyle choices, behaviors and life experiences of parents, grandparents and even great-grandparents, as well as certain environmental toxins, chemicals and infectious agents. Environmental factors can encompass just about everything that isn’t an inherited gene.
Epigenetic changes: DNA methylation and histone modifications
Chemical modifications can occur within the nucleotides within DNA, and alter the template for passing on instructional messages in genes — these epigenetic changes do not change the DNA itself but rather determine whether a certain gene will be expressed. Epigenetic changes can affect the DNA or the histone (i.e., proteins that bind to DNA to form chromatin). Histone changes can influence how chromatin (i.e., complex of DNA and proteins that makes up chromosomes) is arranged and can affect whether or not the DNA will be transcribed.
Two main types of modifications may occur to histones. Histones can be modified by chemical processes that either add an acetyl group to DNA (i.e., acetylation) or add a methyl group to the DNA (i.e., methylation). These epigenetic modifications are sometimes a part of normal health and development, but they can also lead to abnormal epigenetic changes that alter how a gene is expressed by either silencing or activating a gene.
The Human Epigenome Project
The Human Epigenome Project (HEP) is a multinational effort that aims to identify, catalog and interpret methylation patterns of all human genes. This large-scale project aims to identify the missing links between our genes and the environment and their role in human pathology. Having an understanding of the epigenetic factors that are not dependent on gene sequence will significantly advance our ability to understand and diagnose human disease. Similar to the Human Genome Project that gave us the genetic blueprint for life, the Epigenome Project will be fundamental for understanding the biological changes in response to external and internal stimuli that result in disease.
Epigenetic influences on mental health
Behavioral and mental health factors may also be affected by epigenetic changes. Dr. Arturas Petronis, a senior scientist in the neuroscience research department and head of the Krembil Family Epigenetics Laboratory at the Centre for Addiction and Mental Health in Toronto is among the first to investigate the links between epigenetics and psychiatry. Petronis and his colleagues have conducted numerous epigenetic studies to help identify the causes of complex diseases such as schizophrenia, which they believe having a better understanding of these epigenetic changes may also widen the scope for novel diagnostic and therapeutic approaches.
Sovereign Health of Texas offers pharmacogenetic testing for patients receiving behavioral health treatment services for addiction and co-occurring disorders. For more information on pharmacogenetic testing or programs offered at Texas, please contact our 24/7 helpline to speak to a member of our team.