genetic testing
-
What is genetic testing?
Genetic testing identifies gene variations linked to health, ancestry, and inherited disorders. It's typically done after reviewing medical history and family records to determine if a condition is inherited. Genetic tests analyze chromosomes, genes, DNA, enzymes, hormones, or amino acids. DNA analysis is powerful because it can be performed using tiny samples from almost any tissue. Genetic testing is also increasingly used in genealogy, the study of family origins and history.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is genetic testing done?
Genetic testing identifies gene variations linked to health, ancestry, and inherited disorders. Tests are typically done after considering a medical history, physical exam, and family pedigree.
Genetic tests use chemical, radiological, and electrodiagnostic procedures. They may include cytogenetic analyses to investigate chromosomes, molecular assays to investigate genes and DNA, or biochemical assays to investigate enzymes, hormones, or amino acids. Tests like polymerase chain reaction (PCR) and recombinant DNA technology have high rates of sensitivity and specificity and can detect even one-base-pair changes in DNA. DNA can be amplified from various sources and used to detect gene mutations in tumors and inherited disorders.
6 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Why do people get genetic tests?
People undergo genetic testing for various reasons, including identifying gene variations linked to health, disease, and ancestry, as well as diagnosing inherited diseases and disorders. Genetic tests involve analyzing chromosomes, genes, and DNA.
Personalized medicine utilizes genetic testing to assess disease risk based on family history and to inform decisions about screening and prevention. For instance, individuals with a family history of Lynch syndrome may undergo genetic testing to detect causative mutations, enabling early detection and potentially life-saving interventions.
Moreover, screening for mutations like BRCA empowers individuals to make proactive decisions about their health, including lifestyle changes and prophylactic surgeries. Genetic testing can also determine if parents are carriers of inherited diseases. Newborns are screened for genetic disorders to enable early intervention and prevent irreversible damage.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What can genetic testing tell us about our health?
Genetic testing identifies gene variations linked to health, ancestry, and inherited disorders. It involves analyzing chromosomes, genes, and DNA. Genetic testing can assess disease risk based on family history, informing decisions about screening and prevention. For example, detecting mutations related to Lynch syndrome can lead to early detection and potentially life-saving measures.
However, ethical concerns exist regarding genetic privacy and potential discrimination. The Genetic Information Nondiscrimination Act (GINA) in the U.S. aims to protect genetic privacy and prevent discrimination based on genetic information. Predictive testing for late-onset conditions can be traumatic, requiring genetic counseling to ensure informed decisions.
6 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How can genetic testing help doctors make medical decisions?
Genetic testing helps doctors make informed medical decisions by identifying gene variations linked to health, disease, and ancestry. It can be used to assess a patient’s risk for a disease based on family history and to determine if they should undergo genetic testing.
For example, detecting mutations through genetic testing can inform decisions about screening for hereditary colorectal cancer, allowing for early disease detection and potentially saving lives. Genetic testing can also assist in the early diagnosis of hereditary forms of breast, ovarian, and prostate cancer. In addition, variations in drug-metabolizing enzymes can be identified through genotyping, which helps guide decisions about the appropriate drug dosage needed to achieve the desired effect. Genetic counseling is advisable before predictive testing to ensure individuals understand their risk and can make informed decisions.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some ethical concerns about genetic testing?
Genetic testing raises several ethical concerns, including potential discrimination and privacy violations. Genetic Information Nondiscrimination Act (GINA) exists in the United States and similar laws are in place in other parts of the world to protect genetic privacy and prevent discrimination based on genetic information.
However, challenges remain, such as balancing privacy within a family with the ethical need to inform individuals who are at risk for a particular genetic disease. Predictive testing for late-onset conditions can be traumatic, especially when no treatments are available. There are also concerns about reproductive decisions, such as using preimplantation genetic diagnosis, which may be viewed as genetic selection. Genetic counseling aims to address these issues by helping individuals understand their risks and options, empowering them to make informed decisions.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
genetic testing, any of a group of procedures used to identify gene variations associated with health, disease, and ancestry and to diagnose inherited diseases and disorders. A genetic test is typically issued only after a medical history, a physical examination, and the construction of a family pedigree documenting the genetic diseases present in the past three generations have been considered. The pedigree is especially important, since it aids in determining whether a disease or disorder is inherited and likely to be passed on to subsequent generations. Genetic testing is increasingly being used in genealogy, the study of family origins and history.
Genetic mutations
A genetic disorder can occur in a child with parents who are not affected by the disorder. This situation arises when a gene mutation occurs in the egg or sperm (germinal mutation) or following conception, when chromosomes from the egg and sperm combine. Mutations can occur spontaneously or be stimulated by environmental factors, such as radiation or carcinogens (cancer-causing agents). Mutations occur with increasing frequency as people age. In men this may result from errors that occur throughout a lifetime as DNA (deoxyribonucleic acid) replicates to produce sperm. In women nondisjunction of chromosomes becomes more common later in life, increasing the risk of aneuploidy (too many or too few chromosomes). Long-term exposure to ambient ionizing radiation may cause genetic mutations in either gender. In addition to these exposure mutations, there also exist two broad classes of genes that are prone to mutations that give rise to cancer. These classes include oncogenes, which promote tumour growth, and tumour-suppressor genes, which suppress tumour growth.
Types of diagnostic genetic tests
Chemical, radiological, histopathologic, and electrodiagnostic procedures can diagnose basic defects in patients suspected of genetic disease. Genetic tests may involve cytogenetic analyses to investigate chromosomes, molecular assays to investigate genes and DNA, or biochemical assays to investigate enzymes, hormones, or amino acids. Tests such as amino acid chromatography of blood and urine, in which the amino acids present in these fluids are separated on the basis of certain chemical affinities, can be used to identify specific hereditary or acquired gene defects. There also exist numerous genetic tests for blood and blood typing and antibody determination. These tests are used to isolate blood or antibody abnormalities that can be traced to genes involved in the generation of these substances. Various electrodiagnostic procedures such as electromyography are useful for identifying defects in muscle and nerve function, which often result from inherited gene mutations.
" height="20" alt="HEW Logo">
Prenatal diagnosis
Prenatal screening is performed if there is a family history of inherited disease, the mother is at an advanced age, a previous child had a chromosomal abnormality, or there is an ethnic indication of risk. Parents can be tested before or after conception to determine whether they are carriers.
A common prenatal test involves screening for alpha-fetoprotein (AFP) in maternal serum. Elevated levels of AFP are associated with neural tube defects in the fetus, including spina bifida (defective closure of the spine) and anencephaly (absence of brain tissue). When AFP levels are elevated, a more specific diagnosis is attempted, using ultrasound and amniocentesis to analyze the amniotic fluid for the presence of AFP. Fetal cells contained in the amniotic fluid also can be cultured and the karyotype (chromosome morphology) determined to identify chromosomal abnormality. Cells for chromosome analysis also can be obtained by chorionic villus sampling, the direct needle aspiration of cells from the chorionic villus (future placenta).
Women who have had repeated in vitro fertilization failures may undergo preimplantation genetic diagnosis (PGD). PGD is used to detect the presence of embryonic genetic abnormalities that have a high likelihood of causing implantation failure or miscarriage. In PGD a single cell is extracted from the embryo and is analyzed by fluorescence in situ hybridization (FISH), a technique used to identify structural abnormalities in chromosomes that standard tests such as karyotyping cannot detect. In some cases DNA is isolated from the cell and analyzed by polymerase chain reaction (PCR) for the detection of gene mutations that can give rise to certain disorders such as Tay-Sachs disease. Another technique, known as comparative genomic hybridization (CGH), may be used alongside PGD to identify chromosomal abnormalities.
Advances in DNA sequencing technologies have enabled scientists to reconstruct the human fetal genome from genetic material found in maternal blood and paternal saliva. This in turn has raised the possibility for development of prenatal diagnostic tests that are noninvasive to the fetus but capable of accurately detecting genetic defects in fetal DNA. Such tests are desirable because they would significantly reduce the risk of miscarriage that is associated with procedures requiring cell sampling from the fetus or chorionic villus.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
Karyotyping
Chromosomal karyotyping, in which chromosomes are arranged according to a standard classification scheme, is one of the most commonly used genetic tests. To obtain a person’s karyotype, laboratory technicians grow human cells in tissue culture media. After being stained and sorted, the chromosomes are counted and displayed. The cells are obtained from the blood, skin, or bone marrow or by amniocentesis or chorionic villus sampling, as noted above. The standard karyotype has approximately 400 visible bands, and each band contains up to several hundred genes.
When a chromosomal aberration is identified, it allows for a more accurate prediction of the risk of its recurrence in future offspring. Karyotyping can be used not only to diagnose aneuploidy, which is responsible for Down syndrome, Turner syndrome, and Klinefelter syndrome, but also to identify the chromosomal aberrations associated with solid tumours such as nephroblastoma, meningioma, neuroblastoma, retinoblastoma, renal-cell carcinoma, small-cell lung cancer, and certain leukemias and lymphomas.
Karyotyping requires a great deal of time and effort and may not always provide conclusive information. It is most useful in identifying very large defects involving hundreds or even thousands of genes.