by Caroline Relton
Epidemiology, a well established cornerstone of medical research, is a group level discipline that aims to decipher the distribution and causes of diseases in populations. Epigenetics, perceived by many as the most fashionable research arena in which to be involved, is a mechanism of gene regulation. What brings these perhaps unlikely partners together?
Epigenetic processes are key features in gene regulation. Epigenetic patterns are laid down in early development and are moulded through in utero and early postnatal life and continue to show some degree of plasticity across the lifecourse. Many environmental, behavioural, nutritional and lifestyle factors are believed to influence epigenetic patterns and in some case the evidence base is substantial. What is less clear is the role of this environmentally modifiable ‘epigenome’ on disease risk in populations. This is where epidemiology can help. A good starting point for an epidemiological engagement with epigenetics is clearly identified by Nessa Carey, in her recent popular science book The Epigenetics Revolution:
“The majority of non-infectious diseases that afflict most people take a long time to develop, and then remain as a problem for many years if there is no cure available. The stimuli from the environment could theoretically be acting on the genes all the time in the cells that are acting abnormally, leading to disease. But this seems unlikely, especially because most of the chronic diseases probably involve the interaction of multiple stimuli with multiple genes. It’s hard to imagine that all these stimuli would be present for decades at a time. The alternative is that there is a mechanism that keeps the disease-associated cells in an abnormal state, i.e. expressing genes inappropriately. In the absence of any substantial evidence for a role for somatic mutation, epigenetics seems like a strong candidate for this mechanism”.
Recent literature points to a role for epigenetic variation in a range of diseases including neurological disease, cardiovascular disease, osteoarthritis and obesity but in most instances these are correlations without robust evidence of causality. Indeed, epigenetics is often proffered as the answer to many unresolved causes of disease. The enthusiasm for establishing whether epigenetic mechanisms link the environment with disease development must be tempered by the knowledge that the epigenome is dynamic and has as much potential to respond to disease as respond to the environment. Therefore it is very difficult to disentangle cause from consequence when studying epigenetic variation and disease.
This is just one of the many challenges that face researchers interested in understanding the role of epigenetics in common complex disease. Other challenges include the differences in interpretation of the term ‘epigenetics’ itself – in a field that attracts cell, developmental and evolutionary biologists, epidemiologists and bioinformaticians, amongst others, it is unsurprising that epigenetics means different things to different people and discussions of its relevance to disease can sometimes suffer misinterpretation.
The methods at our disposal to accurately measure epigenetic variation and in turn assess the impact this has upon disease risk are still being developed and there is much to do in this arena with respect to when, where and how to look at the epigenome. The complexity and interplay of multiple factors in determining disease risk is the bread and butter of epidemiology, including how to measure exposures and outcomes meaningfully and how to interpret information with respect to its impact and relevance to human populations. In this regard epidemiology has much to offer the field of epigenetics in overcoming current challenges. The marriage of these two fields also presents opportunities for epidemiologists, as it presents considerable scope for enhancement and development of epidemiological methods, for example in causal analysis methods and in statistical approaches to dealing with high dimensional data. The potential for synergy between these fields is extensive.
Epidemiology by no means provides the sole solution but can offer tools that can be applied (and enhanced) to address the many unanswered research questions in the field of epigenetics and its role in the prediction, prevention and treatment of common complex disease. Research activity in this area can only be encouraged and will be an essential process in advancing knowledge and understanding of the causes of many common complex diseases.
Caroline Relton is Senior Lecturer at the Institute of Genetic Medicine, Newcastle University. The International Journal of Epidemiology has granted free access to this special issue on epigenetics for a limited time.