ted variation in iron transport, iron intake and iron loss. Similarly, breast cancer in some individuals could result from the interaction between an inherited mutation in the BRCA1 gene and yet-to-be-described cofactor(s), including other genes and modifiable risk factors. When this book's authors refer to "genetic disorders," they are usually referring to conditions in which a single gene with high penetrance or a chromosomal abnormality have been implicated. It is implicit, however, that genetic factors do play a role in the etiology of virtually all human diseases, even those that are traditionally not thought of as "genetic" (e.g., infectious and occupational diseases).
Thus, an important theme of this book is the need to identify the modifiable risk factors for disease that interact with the genetic variation and that may be used to help target preventive interventions. Recognition of the need to apply knowledge about the interaction between environment and genetics to health care has been described in the popular press (22).
Finally, an inherent assumption in our discussion of the future of genetics in public health is that much of the delivery of genetic tests and services for disease prevention and health promotion, including adequate family history assessment and genetic counseling, will be done within the context of the broader healthcare system. Managed care organizations will play an important role in integrating genetic services into disease prevention and health promotion activities.
Framework for Integrating Genetic Discoveries into Public Health Functions
A framework for applying essential public health functions in evaluating the relevance of gene discoveries to disease prevention and health promotion was developed as part of the CDC's strategic plan for genetics and public health (11). This framework encompasses four essential public health functions and three critical issues that affect each function (Table 3). The rest of this book is largely organized according to these public health functions and related critical issues. The following provides a brief overview.
I. The Role of Public Health Assessment in Genetics
Public health assessment in genetics relies on scientific approaches to assess the impact of discovered genes on the health of communities. The traditional forms of applied research in public health include surveillance and epidemiology, which are explored in more detail in section II (chapters 6 through 11).
In general, surveillance-the systematic gathering, analysis and dissemination of population data (23)-is needed to determine the population frequency of genetic variants that predispose people to specific diseases, both common and rare; the population frequency of morbidity and mortality associated with such diseases; and the prevalence and effects of environmental factors known to interact with given genotypes in producing disease. Information could be gathered also through broader surveillance of the economic costs of the genetic component of various diseases (e.g., expressed by healthcare costs, hospitalization rates, years of potential life lost and other measures); genetic testing issues (e.g., access to services, quality of tests, usage by providers and potential discrimination); and issues related to interventions (e.g., availability, safety and effectiveness). Examples of existing surveillance and health information systems include the National Health and Nutrition Examination Survey (24), population-based birth defects surveillance systems (25) and cancer surveillance systems (26).
Epidemiology is often viewed as the scientific core of public health. A widely used definition is "the study of the distribution and determinants of health-related states or events in populations, and the application of this study to control health problems" (27). Epidemiologists not only investigate outbreaks of disease in different populations but also conduct studies to determine risk factors for various diseases, identify high-risk subpopulations to which to target prevention and intervention ac