Genetic Tests: How It Works And When They Are Needed

Genetic Tests: How It Works And When They Are Needed
Genetic Tests: How It Works And When They Are Needed

Video: Genetic Tests: How It Works And When They Are Needed

Video: Genetic Tests: How It Works And When They Are Needed
Video: Advanced prenatal genetic testing 2023, March
Anonim

Any genetic analysis - decoding a person's DNA and interpreting the results - consists of several stages. Genetic material is taken from cells: they used to work with blood, now laboratories are increasingly switching to non-invasive methods and isolating DNA from saliva.

The isolated material is sequenced - with the help of chemical reactions and analyzers, it is determined in what sequence the monomers are located in it: this is the genetic code. The resulting sequence is compared with the reference and looking for specific areas corresponding to certain genes. Based on the presence or absence of genes or their changes, a conclusion is made about the test result.

Running a sequencer - a device that decodes a DNA sequence - is very expensive due to the large number of chemicals required. Many DNA samples can be deciphered in one run, but the more there are, the less reliable the result will be for each sample and the lower the accuracy of the genetic test. Therefore, you should contact a trusted laboratory, which will not save on the quality of analysis by increasing the number of samples.

An important point that should be taken into account when obtaining the results of genetic analysis: genetics does not determine everything that happens to our body. Lifestyle and environmental factors play no less important role - ecological situation, climate, amount of sunlight and others.

Unfortunately, Russian companies rarely mention this and limit themselves to listing the benefits of a genetic test. Many also play on the lack of education of patients and impose expensive unnecessary tests.

These are the main cases for which modern genetic testing is applied.

Health issues

First of all, genetics is designed to help in the treatment and prevention of diseases. There are three main groups of cases when genetic analysis will help clarify the diagnosis or prevent a possible disease.

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Diagnostics of viruses and bacteria by the presence of their DNA in the blood

For whom the test. For those who suspect they have a viral or bacterial infection. So, for example, they can diagnose borreliosis with a tick bite - a disease with a wide range of symptoms.

How it works. The DNA of organisms that cause disease is different from that of humans. A blood test is taken from the patient and it is determined whether there is foreign genetic material.

What is important to consider. These are relatively inexpensive tests, because it does not require decoding of the DNA itself, you just need to determine its presence or absence. Such a test will be more accurate than, for example, a search for antibodies (they appear in the blood only after the incubation period), but it is possible only if a specific disease is suspected.

Diagnosis of existing diseases

For whom the test. As a rule, these are complex cases or chronic ailments, the cause of which is not obvious. Then doctors look for possible causes of the disease in the genes and, based on the results, can more accurately diagnose and adjust the treatment.

How it works. Genetic material can be obtained from any patient's cells, including material taken for other analyzes. After decoding the DNA, damaged genes are looked for in the sequence. As a rule, this is not a “blind” search along the entire length, but a study of previously known areas.

What is important to consider. Gene diseases - those that occur due to mutations of just one gene - are quite few. About 92% of diseases that can be found in DNA are multifactorial. This means that mutation is not the only cause of the disease, and adjusting other factors, such as diet or climate, can make it easier.

Prevention of diseases to which there is a predisposition

For whom is the test. Doctors can recommend such an analysis to healthy people who have had repeated cases of various diseases among their relatives, such as, for example, most types of cancer, diabetes mellitus and coronary heart disease. That is, those same multifactorial hereditary diseases, which are also called "polygenic with a threshold effect." Such an analysis can also reveal the likelihood of developing allergies, help adjust the diet depending on the genetic basis of metabolism and select the optimal physical activity.

How it works. In addition to mutations, doctors can also pay attention to gene variations - alleles. When checking the predisposition to certain diseases, a specific section of DNA is analyzed. Comprehensive screening for a range of potential hereditary diseases can involve the entire genome.

What is important to consider. It is not for nothing that these diseases are called "with a threshold effect." This means that the disease will develop only after the body reaches the "threshold". The task of prevention is precisely to prevent this from happening. That is, a positive test for susceptibility to breast cancer does not mean at all that this will happen one hundred percent. Such a result rather serves as a recommendation to be more attentive to yourself, to avoid risk factors and not to neglect regular examinations by a mammologist.

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Family planning

When people want to have a child, they willy-nilly think about his future health. Genetic tests can help in two stages - when planning a pregnancy and during its course.

Planning children

For whom the test. Such a test will help to find out if the child will inherit "dormant mutations" and the risks of congenital pathologies. This is important in case of frequent cases of some kind of disease in the family history of the father and / or mother, or if one of the parents actually has a disease.

How it works. In essence, such tests do not differ from identifying predispositions to diseases in adults, but they simultaneously analyze two parental genomes.

What is important to consider. The complexity of the analysis lies in the fact that it is impossible to find out in advance which genes of the parents will get the child, this is a kind of lottery. Genes always work not by themselves, but in a complex, which makes the number of variations of the unborn child's genome infinite. That is, the test for heredity of the planned offspring is always probabilistic, and even the presence of “bad” mutations in the parents does not make the birth of a healthy baby impossible.

Prenatal diagnosis

For whom the test. This analysis is performed during pregnancy and is needed if congenital abnormalities are suspected. Also, prenatal genetic diagnosis can determine the sex of the unborn child at an early stage of pregnancy and establish paternity.

How it works. For prenatal diagnosis, there are several methods of taking a sample of genetic material, the main of which are chorionic biopsy (taking a piece of fetal tissue) and amniocentesis (taking a sample of amniotic fluid). Recently, it is also practiced to isolate the DNA of the embryo from the mother's blood - a non-invasive prenatal DNA test (NIPT). With in vitro fertilization, preimplantation diagnosis is also possible - DNA is isolated from the embryo cell before it is introduced into the uterus.

What is important to consider. Invasive methods are always a risk. So, the probability of spontaneous abortion after a biopsy reaches 15%, and amniocentesis can lead to infection or detachment of the membranes of the fetus. Both of these methods become possible at a relatively late stage of pregnancy, when the fetal bladder is formed and the embryo is clearly distinguishable on ultrasound, so they should only be used if there are serious suspicions of genetic or chromosomal defects. Non-invasive diagnosis does not have these consequences and can be performed from the ninth week of pregnancy.

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Identifying talents and inclinations

For whom the test. Often, genetic testing companies also ask parents to identify the predisposition of children to certain sports or other activities. Such a test can be useful for young athletes before starting a serious career: according to researchers, 60% of sports success is determined by genes.

How it works. The analysis itself is carried out in the same way as for determining hereditary diseases, only other sections of DNA are examined. To date, about 50 genes are known that are associated with a predisposition to engage in various sports. With other human talents, it is more difficult: for example, a partial genetic nature of absolute pitch has been established, but for the most part this direction is under study.

What is important to consider. Despite the widespread belief that our genes prescribe certain talents and character traits for us, the genetic basis of the psyche is the least explored area in human genetics. Not only diseases can be polygenic - this is the majority of traits in the body (for example, eye color is determined by 15 genes). Information taken out of context may be not only incomplete, but in principle false: it is impossible to determine by one gene whether a child will become an outstanding athlete or not. As for intellectual abilities and character traits, it still lies in the field of assumptions. Finally, if the result of a genetic test "predicts" the child's success in some path, this can exert psychological pressure on the parents and prevent the child from deciding on his own plans for the future. Genes - a recommendationrather than direct indication.

Finding out the origin

For whom the test. Genealogical research grew out of forensics and the popular task of establishing paternity. Today, with the help of genetics, both the determination of the closest relatives and the identification of the ancestral group are available - from which part of the world the genus came many generations ago. Such an analysis serves to solve applied problems of establishing kinship (this is important for such legal issues as inheritance claims) and may interest simply curious people who study family history.

How it works. In the course of life, every person accumulates small changes in DNA - not only in genes, but also in the “non-working” part (and the share of this in our cells is more than 90%). In genealogical genetic analysis, researchers compare the resulting DNA for similarities with others - either with the DNA of potential relatives or with a large database. Such databases can include both ancient DNA and the genetic material of the country's inhabitants. Depending on the country and the genetic laboratory's access to databases, the picture of the analysis may differ in completeness and detail.

What is important to consider. Unlike previous tests, when the patient's DNA was compared with a standard, this is a comparison with the genetic material of other people. Such a procedure raises questions of confidentiality and requires complex legislative regulation. In Iceland, a genetic database has been collected, which contains the decoded DNA of all citizens and permanent residents (the corresponding law was adopted in 1997). In Russia, such a practice is just beginning to emerge, for the examination of kinship requires the consent of all participants and a complex legal procedure. However, "ancient" databases around the world are in the public domain, and anyone can find out about their roots. For example, here, here and here.

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