Elective genetic and genomic testing are DNA tests performed for an individual who does not have an indication for testing. An elective genetic test analyzes selected sites in the human genome while an elective genomic test analyzes the entire human genome. Some elective genetic and genomic tests require a physician to order the test to ensure that individuals understand the risks and benefits of testing as well as the results. Other DNA-based tests, such as a genealogical DNA test do not require a physician's order. Elective testing is generally not paid for by health insurance companies. With the advent of personalized medicine, also called precision medicine, an increasing number of individuals are undertaking elective genetic and genomic testing.
History
Genetic testing for a variety of disorders has seen many advances starting with cytogenetics to evaluate human chromosomes for aneuploidy and other chromosome abnormalities. The development of molecular cytogenetics involving techniques such as fluorescence in situ hybridization (FISH) followed, permitting the detection of more subtle changes in the karyotype. Techniques to determine the precise sequence of nucleotides in DNA by DNA sequencing, notably Sanger sequencing was developed in the 1970s. In the 1980s the DNA microarray appeared, permitting laboratories to find copy number variants associated with disease that are below the level of detection of cytogenetics but too large to be detected by DNA sequencing. In recent years the development of high-throughput or next-generation sequencing has dramatically lowered the cost of DNA sequencing permitting laboratories to evaluate all 20,000 genes of the human genome at once through exome sequencing and whole genome sequencing. A catalogue of the many uses of these techniques can be found in the section: genetic testing. Most elective genetic and genomic testing employs either a DNA microarray or next-generation sequencing.
Historically, all laboratory tests were initiated and ordered by a physician or mandated by a state. Increasingly, patients and families have become more involved in their own health care. One outcome has been the growing availability of elective genetic and genomic testing that are initiated by a patient but still ordered by a physician. Additionally, elective genetic and genomic testing that does not require a physician's order called, direct-to-consumer genetic testing has recently entered the testing landscape.
Testing categories
Genetic testing identifies changes in chromosomes, genes, or proteins; some are associated with human disease. There are many different clinical and non-clinical situations in which genetic testing is used.
Diagnostic testing
Diagnostic testing is used to identify or rule out a specific genetic or chromosomal condition when a particular disorder is suspected based on signs and symptoms present in the patient. Catalogues of more than 50,000 tests available worldwide can be found at GeneTests and Genetic Testing Registry.
Predictive and pre-symptomatic testing
Predictive and pre-symptomatic testing is carried out in individuals who do not have evidence of the disease under investigation. This testing includes Mendelian conditions and polygenic diseases.
Carrier testing
Carrier testing is used to identify people who carry one copy of a gene change (also referred to as a variant or mutation) that, when present in two copies, causes a genetic disorder. Carrier testing is typically offered to individuals who are considering pregnancy or are already pregnant, have a family history of a specific genetic disorder and to people in ethnic backgrounds that have an increased risk of specific genetic conditions.
Pre-implantation genetic diagnosis
Pre-implantation genetic diagnosis (PGD) is used in conjunction with in-vitro fertilization. In-vitro fertilization is the process of combining an egg (oocyte) and sperm outside of the body with intent of fertilization. PGD is the testing of individual oocytes or embryos for a known genetic condition prior to transferring the embryo to the uterus. Used together, IVF and PGD allow for selection of embryos or oocytes presumably unaffected with the condition. PGD can be utilized by individuals or couples who are affected by a condition of genetic origin, or if both individuals are found to be carriers of a recessive genetic condition.