Genetic Testing and Genetic Screening

In response to a further recommendation of the Task Force, the Secretary's Advisory Committee on Genetic Testing (SACGT) was established in June, 1998, by the Department of Health and Human Services to provide oversight of all aspects of genetic testing.SAGCT's report on oversight issues was published in June, 2000 (1, SACGT 2000).In 1983, the report of the U.S. President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research predicted that before the end of the century genetic screening and counseling would become major components of both public health and individual medical care (1, U.S. President's Commission 1983).Following the identification of a gene linked to breast cancer, BRCA1, Dr. Francis Sellers Collins, director of the National Center for Human Genome Research, said that "it is not inconceivable that every woman in America may want to be screened for this gene.The economic, ethical, and counseling issues will be very daunting.'' (6, Breo 1993).While genetic testing for BRCA mutations has been available commercially since 1996, the results of an evaluation done by the Centers for Disease Control and Prevention (CDC) indicated that population-based screening "...is not recommended because of the complexity of test interpretation and limited data on clinical validity and utility."(8, CDC 2004) In 2005, the United States Preventive Services Task Force concurred with the CDC and recommended that only women with a family history of breast and ovarian cancers be referred for BRCA mutation testing.(8, United States Preventive Services Task Force) Educational materials about gene tests and international directories of clinics and laboratories providing genetic testing services can be found on the Web site GeneTests sponsored by the National Institutes of Health, as well as on MedlinePlus: Genetic Testing located on the U.S. National Library of Medicine's Web site.As a greater proportion of the U.S. population lives beyond 85 years of age, interest in genetic testing for end-of-life conditions such as Alzheimer Disease (AD) continues to grow.Stephen G. Post observes that the "too-hopeful" general public has assigned a degree of scientific certainty to the as yet preliminary genetic findings for AD, and that teaching critical thinking skills about genetic testing to the general public is of the highest priority [8, Post and Whitehouse 1998].The OTA defines genetic testing as "the use of specific assays to determine the genetic status of individuals already suspected to be at high risk for a particular inherited condition.The terms genetic test, genetic assay, and genetic analysis are used interchangeably to mean the actual laboratory examination of samples.''In contrast, genetic screening usually uses the same assays employed for genetic testing but is distinguished from genetic testing by its target population (5, OTA 1990).The National Academy of Sciences (NAS) defines screening as the systematic search of populations for persons with latent, early, or asymptomatic disease (1, NAS 1975).Some of the literature annotated for this Scope Note appears to use the terms "testing'' and "screening'' interchangeably.Philip Boyle points out that the language used to describe genetic variation is important and asks what words should be used: "Defects, flaws, deleterious genes, disorders, or the more neutral conditions?Using words such as normal-and its corollary, abnormal--is likely to foster stigmatization and discrimination'' (1, Boyle 1992).Areas of focus in genetic testing include: prenatal diagnosis, newborn screening, carrier screening, forensic screening, and susceptibility screening.Prenatal diagnosis discerns whether a fetus is at risk for various identifiable genetic diseases or traits.Prenatal diagnosis is made using amniotic fluid, fetal cells, and fetal or maternal blood cells obtained during amniocentesis testing; alpha fetoprotein assays or chorionic villus sampling; or ultrasound tomography, which creates fetal images on a screen.Another method, known as fetoscopy, uses a camera on a needle inserted in the uterus to view the fetus.Since prenatal screening began in 1966 (1, U.S. President's Commission 1983), the number of metabolic defects and genetic disorders that can be diagnosed prenatally has expanded greatly.There is also discussion of requiring testing for parents who are participating in an in vitro fertilization program and are at genetic risk.Preimplantation testing of embryos might ensure that only embryos free of genetic disease or problem traits would be placed in the uterus (7, Robertson 1992).Newborn screening involves the analysis of blood or tissue samples taken in early infancy in order to detect genetic diseases for which early intervention can avert serious health problems or death.Newborn screening first came into use in the early 1960s with the ability to test newborns for a rare metabolic disease, phenylketonuria (PKU), which causes mental retardation and can be prevented by following a special diet (1, Capron 1990).Two other examples of newborn screening, in place since the 1970s, are the testing of African-American infants for sickle cell anemia and Ashkenazic Jews for Tay-Sachs disease (1, Reilly 1991).Carrier screening identifies individuals with a gene or a chromosome abnormality that may cause problems either for offspring or the person screened.The testing of blood or tissue samples can indicate the existence of a particular genetic trait, changes in chromosomes, or changes in DNA that are associated with inherited diseases in asymptomatic individuals (5, OTA 1990).Groups tested include persons at risk or a cross-section of the general public for occurrence statistics.Examples of carrier screening include the previously mentioned tests for sickle cell anemia and for Tay-Sachs disease.In the last few years, screening tests have also been developed for cystic fibrosis, Duchenne muscular dystrophy, hemophilia, Huntington's disease, and neurofibromatosis (1, March of Dimes Birth Defects Foundation 1992; 6, Breo 1993).Recently it also has become possible to identify certain cancer prone individuals through genetic testing (1, Li, et al., 1992).Forensic testing, which is the newest area to use information obtained from genetic testing, seeks to discover a genetic linkage between suspects and evidence discovered in criminal investigations.Test results have been presented as proof of innocence or guilt in court cases, and jury verdicts have been based on this type of genetic evidence.Critics note that forensic laboratories often test just once, unlike research laboratories, which test many times, and that mistakes can be made (4, Hoeffel 1990).Concern is expressed, too, about the confidentiality of DNA profiles obtained from criminal investigations and stored in national police databanks (5, Bereano 1990).Debate now centers on standards and quality control, but it is accepted that the technologies accurately detect genetic differences between humans and are "new, powerful tools to clear the innocent and convict the guilty.''Since DNA is unique, many people are reluctant to see such information become part of any national database, which might include information not only about identity but also about proclivity toward disease or behavior (4, OTA 1990).