Genetic epidemiology

Genetic epidemiology is the study of the role of genetic factors in determining health and disease in families and in populations, and the interplay of such genetic factors with environmental factors. Genetic epidemiology seeks to derive a statistical and quantitative analysis of how genetics work in large groups.^[1]

Definition

The use of the term Genetic epidemiology emerged in the mid 1980s as a new scientific field.

In formal language, genetic epidemiology was defined by Newton Morton, one of the pioneers of the field, as "a science which deals with the etiology, distribution, and control of disease in groups of relatives and with inherited causes of disease in populations".^[2] It is closely allied to both molecular epidemiology and statistical genetics, but these overlapping fields each have distinct emphases, societies and journals.^[1]

The Genetic Epidemiology Department of Science (GEMS) defines the field as "the scientific discipline that deals with the analysis of the familial distribution of traits, with a view to understanding any possible genetic basis", that "seeks to understand both the genetic and environmental factors and how they interact to produce various diseases and traits in humans".^[3] The BMJ adopts a similar definition, "Genetic epidemiology is the study of the aetiology, distribution, and control of disease in groups of relatives and of inherited causes of disease in populations."^[4]

History

In an effort to explain disease occurrence, Hippocrates suggested in his essay “On Airs, Waters, and Places” that factors such as behavior and environment may play a role in disease.

In 1662 epidemiology was further developed by the work of John Graunt, who tried to quantify mortality in London using a statistical approach, noting the various factors he thought played a role in high mortality rates.

The grandfather of epidemiology was John Snow, considered the “father of field epidemiology” was the first to use statistics to discover and target the cause of cholera outbreaks in London. He investigated the cases of cholera and plotted them onto a map identifying the most likely cause of cholera, which was shown to be contaminated water wells.

Modern History

Modern genetics began on the foundation of Gregor Mendels work, which spurred a revolution in hereditary throughout the animal kingdom; showing that the factors that define characteristics and traits was controlled by the passage of Genes. The gene variation was shown to affect disease. The work on quantifying factors affecting disease was greatly advance in the late 19th to 20th century. The period since the second world war played the greatest role in the advancement of the field. Studies by Doll and Hill which linked lung and cardiovascular disease to residents in the town of Framingham, Massachusetts.^[5]

In the 1960s and 1970s, epidemiology was used to eradicate all known naturally occurring smallpox worldwide.^[6]

The work of scientists such as Newton Morton helped to form the field of genetic epidemiology as it is known today; through their application of modern genetics to the statistical study of genetics.

Fundamentals

Traditionally, the study of the role of genetics in disease progresses through the following study designs, each answering a slightly different question:^[7]

• Familial aggregation studies: Is there a genetic component to the disease, and what are the relative contributions of genes and environment?
• Segregation studies: What is the pattern of inheritance of the disease (e.g. dominant or recessive)?
• Linkage studies: On which part of which chromosome is the disease gene located?
• Association studies: Which allele of which gene is associated with the disease?

This traditional approach has proved highly successful in identifying monogenic disorders and locating the genes responsible.

More recently, the scope of genetic epidemiology has expanded to include common diseases for which many genes each make a smaller contribution (polygenic, multifactorial or multigenic disorders). This has developed rapidly in the first decade of the 21st century following completion of the Human Genome Project, as advances in genotyping technology and associated reductions in cost has made it feasible to conduct large-scale genome-wide association studies that genotype many thousands of single nucleotide polymorphisms in thousands of individuals. These have led to the discovery of many genetic polymorphisms that influence the risk of developing many common diseases.

Approaches

Genetic epidemiological research follows 3 discreet steps, as outlined by M.Tevfik Dorak:

1. Establishing that there is a genetic component to the disorder.
2. Establishing the relative size of that genetic effect in relation to other sources of variation in disease risk (environmental effects such as intrauterine environment, physical and chemical effects as well as behavioral and social aspects).
3. Identifying the gene(s) responsible for the genetic component.

These research methodologies can be assessed through either family or population studies.^[8]

See also

• Epigenetics
• Genetic disorder
• Mendelian randomization
• Molecular epidemiology
• Mutation
• Population genetics
• Hardy–Weinberg principle
• Population groups in biomedicine

References

Further reading

• Teare, M.D. (2011). Genetic Epidemiology. Springer. ISBN 978-1-60327-415-9. 

External links