Science, medicine, and the future. Genetic epidemiology

What is epidemiology? Changing definitions of epidemiology 1978-2017

CONTEXT

Epidemiology is a discipline which has evolved with the changes taking place in society and the emergence of new diseases and new discipline related to epidemiology. With these evolutions, it is important to understand epidemiology and to analyse the evolution of content of definitions of epidemiology.

OBJECTIVES

The main objective of this paper was to identify new definitions of epidemiology available since 1978. Secondary objectives were to analyse the content of these definitions, to compare them with those used by Lilienfeld and to determine whether changes have taken place over the last forty years.

METHODS

A review of grey literature and published literature was conducted to find the definitions of epidemiology written between 1978 and 2017.

RESULTS

102 definitions of epidemiology were retained. They helped to highlight 20 terms and concepts related to epidemiology. Most of them were already used in the definitions used by Lilienfeld. Five terms were present in more than 50% of definitions from the period 1978 to 2017: "population", "study", "disease", "health" and "distribution". Several developments have occurred: strengthening of the terms "control" and "health" already used, the concept of "disease" was less frequently encountered whereas the concepts "infectious diseases", "mass phenomenon" are no longer used in definitions from 1978 to 2017.

CONCLUSION

This evolution of content of definition of epidemiology is absent from books on epidemiology. A thematic analysis of definitions of epidemiology could be conducted in order to improve our understanding of changes observed.

Three Metaphors to Aid Interdisciplinary Dialogue in Public Health

Within this journal, authors have recently called for or discussed the benefits of interdisciplinary collaboration. However, in practice such collaborations are extremely challenging, and little guidance is available to support researchers' efforts to communicate with colleagues from other disciplines. This article presents three metaphors from the sociology of scientific knowledge that can inform and support consideration and discussion of disciplinary issues. Disciplinary training acts as a "flashlight," highlighting certain features of reality and leaving others in shadow. Our disciplinary sense of normal science is the metaphorical "box" into which we hope nature will fit, determining the manner in which we advance the frontier by recognizing the familiar in the unfamiliar. Finally, scientific training is a "lens" through which the world is perceived and understood. In interdisciplinary and some multidisciplinary contexts, researchers are encouraged to (1) identify the set of fundamental concepts underpinning their approach to public health, (2) discuss methodological choices in terms that do not depend on familiarity with a common tradition of research excellence, and (3) maintain awareness that colleagues from other fields potentially hold different understandings of key public health concepts.

Time pressure and sleep problems due to thoughts about work as risk factors for future sickness absence

Purpose

This study investigated whether time pressure or sleep problems due to thoughts about work are associated with future sickness absence (SA) among women and men employed in different sectors, also when adjusting for confounders including familial factors (genetics and shared environment).

Methods

The study sample included 16,127 twin individuals (52% women), aged 19–47 years who in 2005 participated in an online survey including questions regarding time pressure, sleep, work and health. Register data on SA (> 14 days) were obtained from the National Social Insurance Agency and individuals were followed from date of survey response until 12/31/2013. Associations between time pressure, sleep problems due to thoughts about work and future SA were investigated using logistic regression analyses to assess odds ratios (OR) with 95% confidence intervals (CI).

Results

In total 5723 (35%) individuals had an incident SA spell during follow-up. Sleep problems due to thoughts about work were associated with SA in the fully adjusted model (OR 1.22, CI 1.10–1.36). Stratified by sector, the highest estimate was found for state employees (OR 1.54, CI 1.11–2.13). Familial factors did not seem to influence the associations. We found no statistically significant associations between time pressure and SA. No sex differences were found.

Conclusions

Results indicated that sleep problems due to thoughts about work is a risk factor for future SA. This follows previous research showing that sleep length and sleep disturbances, regardless of reason, are associated with SA. But, experiences of work-related time pressure seem to have no effect on SA.

Smoking and polymorphisms in xenobiotic metabolism and DNA repair genes are additive risk factors affecting bladder cancer in Northern Tunisia

Cancer epidemiology has undergone marked development since the nineteen-fifties. One of the most spectacular and specific contributions was the demonstration of the massive effect of smoking and genetic polymorphisms on the occurrence of bladder cancer. The tobacco carcinogens are metabolized by various xenobiotic metabolizing enzymes, such as the super-families of N-acetyltransferases (NAT) and glutathione S-transferases (GST). DNA repair is essential to an individual's ability to respond to damage caused by tobacco carcinogens. Alterations in DNA repair genes may affect cancer risk by influencing individual susceptibility to this environmental exposure. Polymorphisms in NAT2, GST and DNA repair genes alter the ability of these enzymes to metabolize carcinogens or to repair alterations caused by this process. We have conducted a case-control study to assess the role of smoking, slow NAT2 variants, GSTM1 and GSTT1 null, and XPC, XPD, XPG nucleotide excision-repair (NER) genotypes in bladder cancer development in North Tunisia. Taken alone, each gene unless NAT2 did not appear to be a factor affecting bladder cancer susceptibility. For the NAT2 slow acetylator genotypes, the NAT2*5/*7 diplotype was found to have a 7-fold increased risk to develop bladder cancer (OR = 7.14; 95% CI: 1.30-51.41). However, in tobacco consumers, we have shown that Null GSTM1, Wild GSTT1, Slow NAT2, XPC (CC) and XPG (CC) are genetic risk factors for the disease. When combined together in susceptible individuals compared to protected individuals these risk factors give an elevated OR (OR = 61). So, we have shown a strong cumulative effect of tobacco and different combinations of studied genetic risk factors which lead to a great susceptibility to bladder cancer.

Prediction of recurrence-free survival in postoperative non-small cell lung cancer patients by using an integrated model of clinical information and gene expression

PURPOSE

One of the main challenges of lung cancer research is identifying patients at high risk for recurrence after surgical resection. Simple, accurate, and reproducible methods of evaluating individual risks of recurrence are needed.

EXPERIMENTAL DESIGN

Based on a combined analysis of time-to-recurrence data, censoring information, and microarray data from a set of 138 patients, we selected statistically significant genes thought to be predictive of disease recurrence. The number of genes was further reduced by eliminating those whose expression levels were not reproducible by real-time quantitative PCR. Within these variables, a recurrence prediction model was constructed using Cox proportional hazard regression and validated via two independent cohorts (n = 56 and n = 59).

RESULTS

After performing a log-rank test of the microarray data and successively selecting genes based on real-time quantitative PCR analysis, the most significant 18 genes had P values of <0.05. After subsequent stepwise variable selection based on gene expression information and clinical variables, the recurrence prediction model consisted of six genes (CALB1, MMP7, SLC1A7, GSTA1, CCL19, and IFI44). Two pathologic variables, pStage and cellular differentiation, were developed. Validation by two independent cohorts confirmed that the proposed model is significantly accurate (P = 0.0314 and 0.0305, respectively). The predicted median recurrence-free survival times for each patient correlated well with the actual data.

CONCLUSIONS

We have developed an accurate, technically simple, and reproducible method for predicting individual recurrence risks. This model would potentially be useful in developing customized strategies for managing lung cancer.

Cardiomyopathy in Africa: heredity versus environment

Unlike other parts of the world in which cardiomyopathy is rare, heart muscle disease is endemic in Africa. The major forms of cardiomyopathy in Africa are dilated cardiomyopathy (DCM) and endomyocardial fibrosis (EMF). Whereas DCM is a major cause of heart failure throughout the continent, EMF is restricted to the tropical regions of East, Central, and West Africa. Although epidemiological studies are lacking, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy seem to have characteristics similar to those of other populations elsewhere in the world. Recent advances in the genetic analysis of DCM in other parts of the world indicate that it is a genetically heterogeneous disorder in which some cases have a Mendelian cause and others have a non-genetic or multifactorial cause. This heterogeneous pattern of inheritance has been confirmed in small studies that have been conducted so far in Africa. The advent of human immunodeficiency virus infection and its association with cardiomyopathy has emphasised the role of inflammatory agents in the pathogenesis of DCM. By contrast with DCM in which some cases have major genetic contributions, there is scanty evidence for the role of genetic factors in the aetiology of EMF. Although the pathogenesis of EMF is not fully understood, it appears that the conditioning factor may be geography (in its widest sense, to include climate and socio-economic status), the triggering factor may be an as yet unidentified infective agent, and the perpetuating factor may be eosinophilia. There is a need for renewed effort to identify genetic and non-genetic factors in EMF and other forms of heart muscle disease that are prevalent on the continent of Africa.

Gene expression profiling on lung cancer outcome prediction: present clinical value and future premise

DNA microarray has been widely used in cancer research to better predict clinical outcomes and potentially improve patient management. The new approach provides accurate tumor classification and outcome predictions, such as tumor stage, metastatic status, and patient survival, and offers some hope for individualized medicine. However, growing evidence suggests that gene-based prediction is not stable and little is known about the prediction power of gene expression profiles compared with well-known clinical and pathologic predictors. This review summarized up-to-date publications in microarray-based lung cancer clinical outcome prediction and conducted secondary analyses for those with sufficient sample sizes and associated clinical information. Among the most commonly used analytic approaches, unsupervised clustering mainly recaptures tumor histology and provides variable degrees of prediction for tumor stage, lymph node status, or survival. Overall, most studies lack an independent validation. Supervised learning and testing generally offer a better prediction. Noted is that when conventional predictors of age, gender, stage, cell type, and tumor grade are considered collectively, the predictive advantage of the gene expression profiles diminishes. We conclude that outcome prediction from gene expression signatures selected by current analytic approaches can be mostly explained by well-known conventional predictors, particularly histologic subtype and grade of differentiation. A strategy for establishing independent or more accurate signatures is commented.

Genomics, genetic epidemiology, and genomic medicine

Medical science is on the threshold of unparalleled progress as a result of the advent of genomics and related disciplines. Human genomics, the study of structure, function, and interactions of all genes in the human genome, promises to improve the diagnosis, treatment, and prevention of disease. This opportunity is the result of the recent completion of the Human Genome Project. It is anticipated that genomics will bring to physicians a powerful means to discover hereditary elements that interact with environmental factors leading to disease. However, the expected transformation toward genomics-based medicine will occur over decades. It will require efforts of many scientists and physicians to begin now to sort out the vast amounts of information in the human genome and translate it to meaningful applications in clinical practice. Meanwhile, practicing physicians and health professionals need to be trained in the principles, applications, and limitations of genomics and genomic medicine. Only then will we be in a position to benefit patients, which is the ultimate goal of accelerating scientific progress in medicine. In this inaugural article, we introduce and discuss concepts, facts, and methods of genomics and genetic epidemiology that will be drawn on in the forthcoming topics of the clinical genomics series.

GENETIC TESTING IN PRIMARY CARE

Rapid advances in genetic research are leading to an expanding array of genetic tests. Primary care providers will increasingly be challenged to identify patients whose symptoms, physical findings, or family history indicate the need for genetic testing, and to determine how to use genetic information most effectively to improve disease prevention. In addressing these challenges, practitioners will need to consider the range of different uses of genetic testing, including diagnosis in symptomatic and asymptomatic people, risk assessment, reproductive decision-making, and population screening. They will need a set of core skills and knowledge to evaluate family history and to recognize clinical findings that indicate genetic risk. At the same time, the primary care perspective will contribute to the evaluation of appropriate uses of genetic testing. A partnership between medical genetics and primary care will help to ensure the development of effective policies, educational tools, and practice guidelines for the coming era of genomic health care.

Establishing a set of mental health indicators for Europe

AIMS

This review presents the background work for developing a set of mental health indicators as part of a comprehensive health monitoring system in the European Union. The review focuses on the appraisal of mental health at population level with special emphasis on assessments that could be useful for mental health promotion.

METHODS

A functional model of mental health is used to delineate variables important for a set of mental health indicators. Variables that are not possible to monitor at population level are not discussed here. Literature searches were conducted through the MEDLINE, PSYCHLIT, and SOCIOLOGICAL ABSTRACTS databases and available textbooks.

RESULTS

The review presents findings from research seeking associations between mental health and ill health and different individual, social, economic, ecological, and service-related characteristics. Specific domains as key starting points in establishing a set of mental health indicators are outlined according to the research findings.

CONCLUSION

A set of mental health indicators can enhance the visibility of mental health issues in the European context. Ultimately the indicators could be used in estimating how the targets set for health policies are met, and whether there has been a measurable decrease in disability, suffering, and disease.

Genetic aspects and genetic epidemiology of parasomnias

Parasomnias are undesirable phenomena associated with sleep. Many of them run in families, and genetic factors have been long suggested to be involved in their occurrence. This article reviews the present knowledge of the genetics of the major classical behavioral parasomnias as well as present results from genetic epidemiological studies. The level and type of evidence for genetic effects varies much from parasomnia to parasomnia. The genetic factors are best established in enuresis, with several linkages to chromosomal loci, but their functions are not so far known. Environmental causes and gene-environment interactions are most probably also of great importance in the origin of complex traits or disorders such as parasomnias.

Embryonic and fetal cells which are not diseased or defective; possible sources of genes for disease prevention or treatment

Cancer and other diseases may be a natural biological event, the activities of which may be dependent on the constitution of the individual. Where fetal and embryonic cells are not diseased or faulty or defective, they may be useful as therapies against cancer and other diseases.

[Role of host response during severe bacterial infection]

Explosion of knowledge both in human genomics and in host inflammatory response explains the increasing interest in infectious disease genetics over the last 5 years. However, twin and adoptee studies have suggested more than 15 years ago, that host genetic factors are major determinants of susceptibility to infectious diseases in humans. Recently, candidate gene studies (association studies) and human genomewide analysis have been used to identify infectious diseases susceptibility and resistance genes. Rarely, a single gene defect has been directly related to devastating consequences such as interferon-gamma receptor mutations leading to fatal infections with ubiquitous mycobacteria. For clinical practice, gene polymorphisms of specific host immune defence elements appear to be of major importance. These genetic variants, which modify the regulation or function of the mediators, have been associated with susceptibility and/or outcome of severe sepsis and septic shock. All steps of the host response to bacteria may be affected by genetic factors. For example, Fc gamma receptor, Toll like receptor or mannose binding protein mutations have been shown to modify the detection of pathogens leading to pneumococcal severe infections, Gram-negative bacteria septic shock, and meningococcal disease, respectively. Polymorphisms of cytokine genes (TNF-alpha, TNF-beta, IL-1-ra) have been reported to influence the level of secreted mediators and to unbalance the inflammatory cascade. Coagulation response to sepsis may also be affected by gene variants such as the plaminogen activator inhibitor 1 (PAI-1) common functional polymorphism which increases the risk of death from meningococcal infection or severe trauma. The impact of these findings on the understanding of infectious disease pathogenesis and on the design of future preventive and therapeutic strategies should be considerable.

Update on the genetics of the idiopathic inflammatory myopathies

A number of lines of investigation suggest that, as is likely the case for other autoimmune diseases, the idiopathic inflammatory myopathies (IIM) develop as a result of specific environmental exposures in genetically susceptible individuals. Current data imply that multiple genes are involved in the etiology of these complex disorders. Targeted gene studies and whole genome approaches have begun to identify several genetic risk factors for autoimmune diseases, but the rarity and heterogeneity of the IIM have limited our knowledge of their associated genes. Current findings suggest that human leukocyte antigen (HLA) genes on chromosome 6, particularly HLA DRB1*0301 and the linked allele DQA1*0501, have the strongest associations with all clinical forms of IIM in white patients. Different HLA alleles, however, may confer risk or protection for myositis in distinct ethnic, serologic, and environmental exposure groups. Non-HLA genetic risk factors, which have been documented for other autoimmune diseases, are now being identified for the IIM. These include polymorphic genes encoding immunoglobulin heavy chains (defined by serologic markers known as Gm allotypes), cytokines and their receptors, and certain proteins that accumulate in the myocyte vacuoles of inclusion body myositis patients. Selected allelic polymorphisms of interleukin-1 receptor antagonist variable number tandem repeats and genes for tumor necrosis factor alpha and interleukin-1 alpha also have recently been associated with IIM. The pathogenic bases for the differences among the many clinically, pathologically and immunologically defined syndromes known as the IIM will be elucidated through a better understanding of the multiple genes that define risks for their development, as well as through investigations of gene-gene and gene-environment interactions.