Genetic Testing and Screening Similarities and Distinctions

Though often used interchangeably, genetic testing and screening are different concepts. Genetic testing refers to medical procedures that determine the presence or absence of a genetic disease, condition, or marker in individual patients (Gostin). Genetic tests involve an examination of chromosomes, DNA molecules, or gene products (such as proteins) to find evidence of certain mutated sequences.

Genetic tests can (1) confirm a diagnosis for a symptomatic individual, (2) assist with presymptomatic diagnosis (e.g., Huntington's disease) or assessment of the risk of development of adult-onset disorders (e.g., Alzheimer's disease), (3) identify carriers of one copy of a gene for a disease in which two copies are needed for the disease to be expressed, and (4) aid in prenatal diagnosis and newborn screening. Hundreds of genetic tests are available to predict diseases in individuals and the population (Secretary's Advisory Committee on Genetic Testing [SAGCT]). Many others are being developed.

Despite their great potential, technical limitations to genetic tests can inhibit the prediction of disease in individuals. A genetic test may not be able to identify every mutation of a gene (which can have mutations in several places along its base pairs) and thus may not indicate an abnormality. Different mutations in a gene have different effects. The cystic fibrosis gene, for instance, has 800 potential mutations with varied effects on health (SACGT). In addition, genetic tests do not measure the complex interactions between genes and environment that contribute to the onset of almost all diseases. As a result, a genetic test is limited in its ability to gauge an individual's susceptibility to causes of mortality such as heart disease accurately.

Screening entails the systematic application of a test to a defined population (Gostin). Genetic screening refers to programs designed to identify persons in a subpopulation whose genotypes suggest that they or their offspring are at higher risk for a genetic disease or condition. In many cases this requires the administration of genetic tests, as defined above. Thus, whereas genetic tests are used to reveal specific propensities among individuals, genetic screening programs help identify rates of genetic diseases or conditions among subpopulations and sometimes can uncover previously unknown or unrecognized conditions. The nature and scope of genetic screening programs vary. Some screening programs are mandatory: Persons must participate in a screening program unless they opt out (where allowed) for religious, philosophical, or other reasons. Most screening programs, however, are voluntary. Persons may choose to participate (opt in) but do not have to.

There are many examples of genetic screening for public health purposes. Women may be screened for genetically related breast cancers. Persons may participate in prenatal genetic screening programs to determine genetic disorders in embryos before implantation. Obstetricians may advise pregnant women in higher-risk groups about specific genetic tests. Fetal karyotyping, for example, can suggest an increased likelihood of carrying a fetus with Down's syndrome among older women. Screenings for conditions such as Tay-Sachs disease and cystic fibrosis are available. Perhaps the most prominent example of genetic screening among a subpopulation is the long-standing public health practice of screening newborns for genetic conditions. Most states require the screening of infants for treatable genetic disorders, particularly phenylketonuria (PKU), subject to refusal on religious or philosophical grounds (New York State Task Force on Life and the Law). Some statutes deem newborn screening voluntary, although in practice it almost always is done in the interest of protecting an infant's health.

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