Genetic epidemiology is a discipline that studies the role of genetic factors and their interaction with environmental factors in the distribution and determination of diseases within human populations (e.g cancer, diabetes). In genetic epidemiology, genetic factors are explicitly considered along with environmental factors in the search for causes of disease. This search necessitates incorporating genetic and other biologic markers into traditional epidemiologic studies.
For example: An individual who smokes regularly does not get lung cancer, one of the reasons may be they do not have a genetic susceptibility. However, an individual who never smoked may get lung cancer at an early age because they have a certain genetic make-up.