Welcome to What DNA test?
Here you will find information on:
- How genetic traits are inherited?
- Structure and Function of the DNA Molecule
- What is the DNA?
And a list of available DNA test kits:
An interesting series of short videos on DNA testing:
Genetic testing allows a diagnosis of vulnerability to certain inherited diseases based on genetics, and can also be used to determine a person’s ancestry. Normally, each human being has two copies of each gene, one inherited from his mother and one from his father. The human genome is believed to contain about 20,000 or 25,000 genes. In addition to studying chromosomes at the level of individual genes, genetic testing, in a broader sense, includes biochemical tests to demonstrate the possible presence of genetic diseases, or mutant forms of genes associated with the growth of the danger of developing genetic disorders. Genetic testing identifies changes in chromosomes, genes, or proteins. Most of the time, the test is used to find changes that are associated with inherited diseases. Its results can confirm or rule out a genetic condition that was previously likely or help determine a human’s chances of developing or avoiding a genetic disease. Hundreds of genetic tests are currently in effect, and new ones are being developed.
Since genetic testing can cause ethical or psychological problems, it is usually accompanied by genetic counseling.
Genetic testing is “the analysis of RNA, chromosomes (DNA), proteins, and metabolic processes to detect hereditary diseases, relating to the genotype, mutations, phenotype, or karyotype, for clinical purposes. (Holtzman & Watson 1997). It can provide information about a person’s genes and chromosomes throughout life. The kinds of tests currently available include:
Newborn monitoring: Used after birth to identify genetic diseases that can be treated early. Routine testing of children for disease is the most widely used: millions of babies are tested each year in the United States. All states currently test children for phenylketonuria (a genetic disease that causes mental retardation if left untreated) and congenital hypothyroidism (a disease of the thyroid gland).
Complementary exploration: Used to diagnose or control a specific condition of genes or chromosomes. In many cases, this genetic test is used to confirm a diagnosis when a particular condition is suspected based on mutations and physical symptoms. The diagnostic test can be taken at any time in a person’s life, but it is not available for all genes or all genetic conditions. The results of a diagnostic test can influence a person’s choices about health and disease control.
Carrier testing: Carrier testing is used to investigate people who carry a copy of a genetic mutation that, when present in two copies, causes a genetic disease. This kind of test is offered to people who have a family history of genetic disorders and to people from ethnic groups with a broad risk of possessing specific genetic diseases. If both parents are tested, the test can provide information about a couple’s risk of having a child with genetic problems.
Prenatal Testing: Used to detect changes in the genes or chromosomes of a fetus before birth. This type of test is offered to couples at high risk of having a baby with a genetic or chromosomal disease. In some cases, it can decrease a couple’s uncertainty and help them decide whether to abort the pregnancy. However, it cannot identify all inherited diseases and birth defects.
Predictive testing: These tests are used to detect genetic mutations associated with diseases that appear after birth, or even later. These tests can help people who have a family member who has a genetic disease, but do not have it themselves at the time of the test. Predictive testing can identify mutations that increase a person’s chance of developing diseases with a genetic basis, such as some types of cancer. For example, a person with a BRCA1 mutation has a 65% risk of developing breast cancer. This test can also predict whether a person may have hemochromatosis before any type of symptom appears. The results of these tests can provide information about a person’s risk of developing a specific disease and help make health care decisions.
Genetic fingerprinting: Genetic fingerprinting tests use a person’s DNA strands for legal purposes. Unlike the tests described above, fingerprint tests are not used to detect mutations associated with diseases. These types of tests can identify victims of a crime or catastrophe, clarify or implicate a suspect, or establish biological relationships between people (e.g., paternity).
Investigative examinations: Research examinations include searching for unknown genes, learning how genes work, or improving understanding of genetic diseases. The results of this test, done as part of a research study, are often not available to patients or their doctors.
Diagnostic testing: Used to confirm or dismiss a diagnosis when, because of certain symptoms, a particular disorder is suspected.
Forensic testing: uses DNA sequences to identify an individual for legal reasons. Unlike the previous ones, it is not used to detect mutations associated with diseases. This type of test can identify victims of crimes or catastrophes, rule out or involve suspects of a crime or establish biological relationships between people (paternity for example).
Research testing: includes finding unknown genes, learning how they work, and advancing knowledge of genetic conditions. They are not available to patients.
Samples taken for genetic testing are usually blood, saliva, hair, skin or amniotic fluid. Except in the latter case, where there is a not very high but real risk of miscarriage, the physical risks associated with most tests are very low.
In the forensic field
DNA testing has become the basis of many judicial-police and historical investigations, among them:
Determine paternity or maternity.
Origin of Humanity
Determination of paternity
DNA tests to determine paternity are performed by comparing the DNA sequence of the father, child and mother. The combination of the DNA sequences of the father and mother must result in the sequence of the child; only in this way will there be a certainty, generally of more than 99%, about the paternity of the minor.
Determination of maternity
In some cases what is sought is to determine the maternal genetic line, in this case the mitochondrial DNA is used that the mother transmits to the son / daughter and that only this one transmits to its descendants.
This type of test serves to determine lineages in several generations and was used to know how the human genome has evolved since the appearance of Homo sapiens, through mitochondrial Eve, the first mother who gave birth to modern humanity. Hence, at some generational level, large human populations share the same ancestry and mitochondrial DNA.
Origin of Humanity
On many occasions, historians and sociologists make use of DNA tests to carry out studies on traits and origins of certain populations. In this case it is interesting to know that the great warriors and conquerors of antiquity are now the grandparents of our civilization. In this sense, the National Geographic magazine has published a study that reveals that Genghis Khan may have been one of the grandparents of Humanity.
The DNA Analysis Process
The DNA Analysis process consists of the following steps
Extraction: By means of any cell that has a nucleus DNA can be obtained, either from a drop of blood, a hair or saliva are sufficient. To process these samples, reagents are added that break the cell membranes and release the DNA contained in them, cleaning it of remains such as proteins and other organic compounds.
Amplification: Once the DNA fragments of interest are selected, through a technique called Polymerase Chain Reaction (PCR), the selected fragments are multiplied, obtaining millions of copies.
Electrophoresis: The amplified fragments are separated by means of an electric shock and with the help of powerful automated equipment, the results are visualized in the form of bands or peaks.
Comparison: The sequences obtained in a determined sample are compared with that of another DNA sample and the coincidences are observed to verify if both sequences belong to the same person, correspond to father and son or do not have any relation.
A genetic test is usually done as part of a genetic consultation, and, by mid-2008, there are more than 1200 clinically applicable genetic tests available. Once a person decides to undergo a genetic test, a medical geneticist, genetic consultant, clinician, or specialist can order the test after obtaining a signed consent.
Tests are done based on a sample of blood, hair, skin, amniotic fluid (the fluid that surrounds the fetus during pregnancy), or other similar element. For example, a medical procedure called a “mouth sweep” uses a small brush or cotton swab to take a sample of cells from the inside of the cheek. The sample is sent to a laboratory, where technicians look for specific changes in chromosomes, DNA, or proteins, depending on the suspected disease. The laboratory reports the test results by writing them down to the person’s doctor or genetic counselor.
Routine newborn screening tests are usually done with a blood sample, inserting a syringe into the baby’s heel and placing the blood on a special piece of paper. Unlike other types of genetic testing, in this case a parent receives the results if they are positive.
Interpretation of results
The results of genetic tests are not always simple, as they are often difficult to interpret and explain. When interpreting the results, health professionals should consider the patient’s medical history, family history, and the type of test performed.
A positive result means that the laboratory has found a change in a particular gene, chromosome, or protein of interest. Depending on the purpose of the test, this result may confirm a diagnosis, indicate whether a person is a carrier of a particular genetic mutation, identify the risk of having a disease (such as cancer) in the future, or suggest the need for another test. Because people with family ties have similar genetic material, a positive test often means that the blood relatives of the person involved must also be tested. It is important to note that a positive predictive test result usually cannot establish the exact risk of disease. In addition, health professionals cannot normally use a positive result to predict the progression or severity of diseases.
A negative result means that the laboratory did not find a dangerous copy of the gene, chromosome, or protein that was tested. This result may indicate that a person is not affected by a particular disease, does not have a high risk of contracting it, or does not carry a specific genetic mutation. It is possible, however, that the test could not find a genetic alteration, since many tests cannot detect all of the genetic changes that cause a particular disease. More tests are needed to prove a negative result.
In some cases, a negative result may give information that is not needed. These types of results are called undetermined, uninformative, inconclusive, or ambiguous. Indeterminate results often occur because someone has common, natural variations in their DNA, called polymorphism, that do not affect health. If a genetic test finds a change in DNA that has not been associated with a disease suffered by others, it is difficult to decide whether it is a polymorphism or a mutation caused by a disease. An ambiguous result cannot confirm or rule out a diagnosis, nor can it indicate whether a person is at risk for a particular disease. In some cases, examining other family members may help clarify these kinds of results.
Cost and time
The cost of a genetic test can range from less than a hundred dollars to more than two thousand dollars, depending on the nature and complexity of the test. The cost increases if more than one test is needed or if multiple members of a family must undergo testing to obtain a meaningful result. In countries that have private medical coverage, in many cases, health plans should cover the costs of testing when recommended by a physician.
From the date the mixture is taken, it may take a few weeks or several months for the results to be published. Results for prenatal examinations are often available more quickly because they are important in making decisions about pregnancies.
Genetic testing has potential benefits if the results are both positive and negative. Results can provide a sense of relief from uncertainty and can help people make decisions about controlling and managing their health. For example, a negative result may eliminate the need for check-ups and monitoring in some cases. A positive result can guide the patient to prevention, control, and treatment options. Some test results can also help people make the decision whether or not to have a child. Newborn monitoring can identify genetic diseases early, so treatment can begin as quickly as possible.
Risks and Limitations
The physical risks associated with most genetic testing are very small, particularly in those tests that require only a blood sample or a mouth sweep (a procedure that removes cells from the inside of the cheek). The procedures used to perform prenatal exams carry an unlikely, but existing, risk of miscarriage (abortion) because they require a sample of amniotic fluid or tissue from around the fetus.
Many of the risks associated with genetic testing are emotional, social, or financial consequences of the results. People may feel angry, depressed, anxious, or guilty about receiving them, especially when they reveal risks against which there is no preventive or therapeutic measure. Therefore, laws tend to recognize a “right not to know” such results. In some cases, genetic testing creates stress in a family, because the results may reveal information about other members of the family in relation to whom it has been analyzed. The possibility of discrimination on the basis of genetic information when seeking employment or hiring insurance is also a matter of concern. Some people avoid genetic testing for fear that it will prevent them from purchasing insurance or being hired for a job. Health insurers do not currently require patients to undergo genetic testing in order to be covered, and if they still get the genetic information, they must keep it as confidential as any other private health-related matter.7] Legislation in the United States decreed that health plan administrators are not allowed to deny coverage to a person solely because of his genetic condition, if it demonstrates that he would contract a disease in the future. The legislation also prohibits employers from using genetic information to hire, fire, modify the position or promote their employees. It was signed into law by the president on May 21, 2008..
Genetic testing provides only limited information about an inherited disease. Often the test cannot determine whether a person will suffer symptoms of a disease, how severe the symptoms would be, or how the disease would progress if contracted. Another important limitation is the lack of treatment strategies that exist for various genetic diseases once they are diagnosed.
A geneticist can explain in detail the benefits, risks, and limitations of a particular test. It is important that anyone considering testing understands and discusses all of the factors before making a decision.
Many people are also concerned about the intimate consequences of testing. In the United States, for example, federal law requires this kind of medical information to be confidential.
Consumer Direct Genetic Testing (DTC)
DTC genetic testing is a type of test that is directly accessible to the consumer, without having to be treated by a health professional. Usually, to get a genetic test, health professionals such as doctors get the patient’s permission and order the desired test. These tests, however, allow consumers to circumvent this process and order them themselves. There are a variety of TCD tests, such as breast cancer screening or mutuations linked to fibrosis. The benefits of TCD testing lie in consumer accessibility, active health promotion, and the privacy and confidentiality of genetic information. Possible risks are lack of government regulation and potential misinterpretation of genetic information.
DTC genetic testing has been controversial due to open opposition from the scientific community. Critics of TCD testing argue against it based on the risks involved, uncontrolled advertising and over-marketing, as well as the government’s complete lack of attention to it.
Some advertisements for these tests have been criticized for conveying an exaggerated and inaccurate message about the connection between genetic information and disease risk, using emotions as a sales strategy. An advertisement for a predictive test to prevent breast cancer read: “There is no stronger antidote to fear than information.”
Currently, there is no strong federal regulation that moderates the DTC market. Although hundreds of tests are available, very few are FDA-approved: those sold in packaging sent directly to homes. Because of the nature that most of these tests are mailed in DNA samples, it is difficult for the FDA to devise a form of jurisdiction over the tests, since they are analyzed in suppliers’ laboratories, and are not actually sold as medical devices. In addition, the FDA has not yet officially tested, with scientific evidence, the accuracy of most direct-to-consumer examinations.
On April 24, 2008, the U.S. Senate passed the Genetic Information Non-Discrimination Act with positive votes widely outnumbering 95-0. The act is the first of its kind in the United States to prevent discrimination against people based on their genetic information. This legislation will prohibit health care companies from not covering medical expenses against customers genetically susceptible to long-lasting and costly illnesses.
New York State only allows legal paternity testing and patients must bring a prescription, a judge’s order, or an attorney’s order for the examination.
Some tests available based on DNA analysis
Note: Tests with a single * have been shown to be a risk factor in the development of the disease.
Alpha-1-antitrypsin deficiency (AAT; emphysema and liver disease)
Amyotrophic Lateral Sclerosis (ALS; ALS; Lou Gehrig’s disease; Progressive loss of motor function leading to paralysis and death)
Alzheimer’s disease (APOE; senile dementia variety)
Ataxia telangiectasia (AT; Progressive brain disorder with loss of muscle control)
Gaucher disease (GD; enlarged liver and spleen, bone degeneration)
Inheritance/predisposition to breast and ovarian carcinoma’* (BRCA 1 and 2; breast and ovarian tumors in juvenile age)
Hereditary nonpolyposis colon cancer * (CA; tumors of colon and other organs)
Congenital adrenal hyperplasia (CAH; hormonal deficiency; ambiguous genitality and male pseudohermaphroditism)
Cystic fibrosis (CF; lung and pancreatic disease)
Duchenne muscular dystrophy (DMD; mild-severe muscle weakness, progressive impairment)
Dystonia (DYT; muscle stiffness)
Fanconi anemia, group C’ (FA; anemia, leukemia, skeletal deformities)
V-Leiden factor (FVL; blood emboli)
Fragile X syndrome (FRAX; one of the leading causes of inherited mental retardation)
Hemophilia A and B (HEMA and HEMB; blood disorders)
Hereditary hemochromatosis (FSH; excessive iron buildup disorder)
Huntington’s disease (HD; usually midlife onset; progressive, lethal, degenerative neurological disease)
Myotonic dystrophy (MD; progressive muscle weakness; most common form of muscular dystrophy in adults)
Neurofibromatosis type 1 (NF1; multiple benign tumors of the nervous system that may be disfiguring)
Phenylketonuria (PKU; progressive mental retardation due to enzyme deficiency: correctable by diet)
Polycystic Kidney Disease of the Adult (APKD; Kidney Failure and Liver Failure)
Prader-Willi syndrome (PWS, chromosome 15, neonatal hypotonia, hormonal irregularities, low height, slow metabolism, HC hormonal deficiency, mental retardation, obesity, social disintegration problems, food obsession)
Spinal muscular atrophy
Thalassemias (THAL; anemias – reduced levels of red blood cells)
Some “milestones” in the history of genetic testing
Huntington’s disease (HD)
The 1840s Medical journals describe illnesses with involuntary movements and mental problems, with some family penetration.
1872 George Huntington, a 22-year-old physician, publishes an article describing symptoms and hereditary pattern of Hutington’s disease, based on observations of his father’s patients.
1981 Nancy Wexler begins studies in Venezuelan families, associating the disease to chromosome 4.
1983 HD markers are described.
1986 First HD predictor test.
1993 HD gene at 4p16,3
1938 Dorothy Andersen describes the disease as a defect in the ductus of the exocrine glands.
1951 Salty sweat described in New York City prostrate children, confirming the 17th-century saying that children who taste of salt do not live long.
1986 Several groups of researchers identify a “maracdor” associated with chromosome 7.
1989 CFTR gene discovered at 7q31,2
1997 Follow-up study of 10 confirms that newborn screening with introduction of a diet and antibiotic regimen improves health
2001 The U.S. Institutes of Health, College of Gynecology, and the American College of Genetic Medicine recommend screening before and during pregnancy.
Some possible future problems arising from genetic testing form the plot of the science fiction film Gattaca, and the science fiction animated series Gundam Seed. The idea is that in the future genetic analyses can be carried out in which all the information about the individual and his future health can be shown. Therefore, those individuals born without previous genetic selection and with diseases (or probability of having it) will be treated in a discriminatory way.