Public Health, Genetic Techniques in
Public Health, Genetic Techniques in
As of 2002 more than ten thousand genes have been discovered, and it is estimated that 30,000 to 70,000 human genes will be identified as a result of the Human Genome Project over the following few years. Tests for more than 600 gene variants are already available in medical practice.
Genetic variants, or polymorphisms, are a normal part of genetic viability that may or may not be associated with an increase or decrease in disease risk. With advances in biotechnology, newly characterized genetic variants are being identified at a rapid rate. The challenge will be to ensure the appropriate use of genetic information to improve health and prevent disease in individuals, families, and communities.
The broad mission of public health is to act in society's interest to assure conditions in which people can be healthy. Public health genetics is the application of advances in genetics and molecular biotechnology to improve the public's health and prevent disease. Rapid progress in biotechnology, in sequencing the human genome, and in characterizing gene expression have generated high hopes of finding new ways to improve the public's health through the prevention and treatment of diseases.
At the same time, concerns have been raised about the premature application of such technologies and knowledge. Genetic testing and the understanding of how factors such as hormones , diet, and the environment influence risk in susceptible individuals and human populations present important challenges in the field of public health genetics. Ethical issues, health care policy priorities, risks of discrimination in employment and insurance, and complex psychological aspects within families are also crucial issues in this field.
Public Health Approaches in Genetics
Disease-related genetic variants that have been characterized include those associated with rare diseases as well as those that increase susceptibility to common chronic diseases such as cancer and heart disease. Risk for almost all human diseases results from the interactions between inherited gene variants and environmental factors, including chemical, physical, and infectious agents, as well as behavioral or nutritional factors. Thus it appears reasonable to direct disease-prevention and health-promotion efforts toward individuals at high risk because of their genetic makeup.
To function effectively, public health genetics needs to meet several challenges, including (1) the implementation of research, (2) the evaluation of genetic information and tests, (3) the development, implementation, and evaluation of population interventions, and (4) effective communication and information dissemination. With the realization that all human disease is the result of interactions between genetic variation and the environment (dietary, infectious, chemical, physical, and social factors), it becomes evident that it is important to identify the modifiable risk factors for disease that interact with the genetic variation. This approach can be used to help develop preventive strategies. To be able to deliver appropriate genetic tests and services for disease prevention and health promotion, it is important to integrate genetic services into disease-prevention and health-promotion activities.
Public-health assessment relies on scientific approaches such as surveillance and epidemiology to assess the impact of discovered gene variants on the health of communities. Surveillance, which involves the systematic gathering, analysis, and dissemination of population data, is needed to determine population frequencies of genetic variants that predispose people to specific diseases. This information can be used to assess the population morbidity and mortality associated with such diseases. Surveillance can also be used to determine the prevalence and effect of environmental factors known to interact with given genotypes. Additionally, surveillance can aid in the evaluation of a genetic test in terms of its safety, effectiveness, and cost-effectiveness.
Another example where surveillance can come into play in public health genetics is with infectious diseases and DNA fingerprinting. The ability to characterize pathogenic organisms phenotypically and genotypically can be a powerful approach that provides information important for an antimicrobial surveillance program. It also is a means of providing information that may be useful for understanding pathogenic microorganisms worldwide. With such a program in place, the clonal spread of multiresistant pathogens among patients can be identified.
Epidemiology is the study of the distribution and determinants of health-related states or events in populations and is used to investigate risk factors for various diseases and identify high-risk populations. Epidemiological information can be used to target populations that could benefit most from prevention and intervention actions. Epidemiology is also a tool for evaluating the effect of health programs and services on a population's health. Population-based epidemiological studies are increasingly needed to quantify the impact of gene variants on the risk of disease, death, and disability, and to identify and quantify the impact of modifiable risk factors that interact with gene variants.
Evaluation of Genetic Information and Tests
Genetic tests include the analysis of human DNA, RNA, chromosomes, proteins, and certain metabolites to detect a person's genotype for clinical purposes, including predicting the risk of disease, identifying gene mutation carriers, and establishing prenatal and clinical diagnoses or prognoses. Successful implementation of genetic tests to improve public health requires careful assessment of how and when genetic tests can and should be used to promote health and diagnose and prevent disease. This assessment must include the development of standards and guidelines for assuring quality genetic testing, and the consideration of ethical and legal issues.
Genetic tests need to be evaluated on the basis of several parameters before they can be taken from research laboratory to clinic. It is necessary to assess (1) how good the test is in predicting the underlying genotype, (2) how good the test is in diagnosing or predicting the phenotype or disease, and (3) the benefits and risks of the genetic test and ensuing interventions. Genetic test validity is quantified in terms of sensitivity (the probability of testing positive for the genetic test if there is a gene mutation or if disease occurs), specificity (the probability of testing negative if the genetic mutation is not present or if the disease does not occur), and predictive value (the test's ability to accurately predict disease).
All clinical laboratories in the United States that provide information to referring physicians are certified under the Clinical Laboratory Improvement Act (CLIA) amendments of 1988. The CLIA standards for quality control, proficiency testing, personnel, and other quality assurance practices apply to all genetic tests.
Development, Implementation, and Evaluation of Population Interventions
Recent advances in human genetics have brought high expectations for implementing prevention strategies among genetically susceptible individuals. Yet the clinical use of this information poses risks as well. It is the role of public health to develop intervention strategies for diseases with a genetic component, implement pilot demonstration programs, and evaluate the impact of the intervention on reducing morbidity and mortality in the population. This evaluation includes conducting a needs assessment of genetic services, studying the impact of genetic counseling on public health, and applying prevention-effectiveness principles to genetics programs. Policy analysis of informed consent to genetic testing, stigmatization of individuals and groups, discrimination in employment, and access to insurance need to be considered.
The two recently identified susceptibility genes BRCA1 and BRCA2, which are associated with a high risk of developing breast and ovarian cancers, illustrate some of the complexities individuals from high-risk families face. Studies to determine the efficacy of prophylactic surgeries, chemoprophylactic strategies, and other preventive measures have not been conclusive, leaving individuals from high-risk families—and those who are carriers of mutations—with complex decisions concerning genetic testing and medical intervention.
Newborn screening illustrates the evolution of effective genetic-screening programs. Recognizing the potential importance of phenylketonuria screening over forty years ago, the Children's Bureau (now called the Maternal and Child Health Bureau) sponsored a multistate urine-screening program. The initial outcome was that 30 percent of infants remained untested due to inadequate specimen-collection and delivery. There was sometimes a false-positive reading. Improvements were made, and today a single drop of blood, rather than a urine sample, is sufficient for eight to ten assays for metabolic-disease indicators, along with genetic and infectious information about the mother.
Another example of an evolving genetic-screening program involves the common abnormal hemoglobin "S," or sickle hemoglobin, detected in newborn-screening programs in the United States. This hemoglobin is the defining characteristic for sickle cell disease. The first statewide screening program was established in 1975. Widespread acceptance and implementation was lacking until after a 1986 study showed the efficacy of daily oral penicillin prophylaxis in preventing infection among young children with sickle cell anemia. The efficacy of sickle cell screening was demonstrated through epidemiological efforts to evaluate pediatric outcomes after newborn screening, by demonstrating that mortality rates declined from 1968 to 1992, particularly in cohorts of sickle cell patients.
Communication and Information Dissemination
The fourth public-health function in genetics is developing and applying communication principles and strategies related to advances in human genetics, interventions, and genetic tests and services, as well as in interventions, the ethical, legal, and social issues related to these topics. Public health agencies can play a role in translating the very complex information related to genetics and disease prevention to health care workers and the public. An appropriate mix of mechanisms should be used to disseminate information, including distance-based interactive meetings, information centers, and electronic communication.
In summary, four public health functions for genetics have been outlined that underscore the complexities involved in public health genetics. All are carried out by efforts among various groups, including partnerships and coordinated efforts among federal, state, and local agencies, the public and private sectors, and the public-health, medical, and academic sectors, with various levels of community and consumer involvement. Annual national meetings on genetics and public health facilitate these efforts.
see also Antibiotic Resistance; Cancer; Diabetes; Disease, Genetics of; Genetic Discrimination; Genetic Testing; Hemoglobinopathies; Metabolic Disease; Prenatal Diagnosis.
Joellen M. Schildkraut
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