Every person has thousands of genetic mutations that, under certain conditions, can cause serious diseases, including cancer. Some of the bad genes inherited from their parents, while others arose spontaneously at the stage of embryo formation. And if a gene breakdown is almost impossible to fix, then it is real now to prevent the transmission of mutations to children. RIA Novosti tells how medical genetics help create a generation of healthy people.
“In my practice, there was one large family from Samara who suffered from hereditary motor-sensory neuropathy (HMSN). This disease is unpleasant, but not fatal. The first symptoms appear in childhood; by the age of sixty, the patient is already in a wheelchair. It took us about fifteen years to identify the gene that causes the disease. The molecular cause of the disease was identified in 2015. Six early prenatal diagnostics have already been carried out for different branches of this family. Unfortunately, not everyone has a favorable prognosis. In this case, the pregnancy is terminated. But as a result, all these people gave birth to healthy babies. Imagine, five generations of the family suffered from HMSN, and their descendants will no longer have this mutation,”says Olga Shchagina, a laboratory geneticist.
She heads the laboratory of molecular genetic diagnostics at the Medical Genetic Research Center (MGSC). It is here, in the holy of holies of Russian medical genetics, that the genomes of Russians are decoded in order to find a time bomb in their DNA. The laboratory occupies two floors of the Moscow State Scientific Center and consists of several isolated rooms. Biological samples taken from a patient (most often blood) will pass through each of them before the doctor knows what is hidden in the genes.
DNA cloud
First, laboratory workers isolate DNA from the nucleus of cells, adding substances that destroy the cell membrane to the blood. The resulting DNA is purified from degradation products using isopropyl and ethyl alcohol.
"Wait, now you will see everything," Shchagina smiles, gently rocking a small test tube with a colorless alcohol solution.
From smooth rhythmic movements in the middle of the test tube, a small white cloud forms.
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“This is DNA. It is colorless, but this is how we can see it for a moment,”she explains.
My attempts to photograph the spiral are unsuccessful, the cloud disappears as quickly as it formed. A test tube with a clear liquid and the acid contained in it is sent to a centrifuge, which will separate the biological molecule from alcohols.
Spontaneous chemical changes in the DNA structure lead to mutations / Depositphotos / rob3000.
Multiply and read
A few minutes later, laboratory workers take out tubes with purified DNA from the centrifuge and take them to another room, where the molecule will be multiplied, marked and brought to a state where it can be read in a sequencer - a cipher machine of the genome.
“If we want to read a small piece of a gene, then we do Sanger sequencing. By the way, it was in this way in 2003 that the sequence of human DNA was first deciphered. We break a gene into small fragments, propagate them using the polymerase chain reaction, and get a very large number of copies for research. This method works when we understand where to look. For example, it is known that phenylketonuria is caused in 95 percent of cases by a mutation in the PAH gene. If you need to read several genes at once, or even a complete genome, then new generation sequencing is used,”says Shchagina.
Several small gray devices with built-in displays in a spacious room on the first floor of the MGNTs are the latest generation sequencers. They are managed by the fragile Olga Mironovich, a researcher at the DNA diagnostics laboratory of the Moscow State Scientific Center.
“We mix reagents with prepared DNA samples, insert them into the sequencer, and put a special chip there. Reagents and DNA are transferred to the chip, and all this is photographed many, many times. The software transforms the captured images into data that can be read and interpreted. Mironovich carefully closes the lid of the device and starts the sequencer.
“This particular DNA will be deciphered in twenty-one hours. Then bioinformatics will interpret the results,”she adds.
Learned to read, but not always understand
“The analysis of the exome, that is, the genes responsible for coding proteins, takes at least three weeks. This is if everything went well at all stages and it is more or less clear from the clinical history what to look for. In Russia, and in the whole world, there are not so many specialists who are able to understand the decoded genes,”explains geneticist Oksana Ryzhkova, head of the Center for Shared Use of the Moscow State Scientific Center.
It is to her and her employees that the data from the sequencer gets to after it finishes working.
“Look, I have on my computer the results of decoding the patient's clinical exome - 6300 genes, the pathogenic variants of which lead to the development of hereditary diseases. These are the changes identified in comparison with the reference genome (the genome standard compiled by scientists as a common representative example of the genetic code). A total of 13,129 replacements. It is very difficult to find out which of these options is the cause of the disease. Therefore, we connect to international databases, where both pathogenic variants of genes and diseases associated with them, and variants described as benign, not leading to clinical manifestations, are laid out, and we compare our variants with them. After the stage of "filtration" by pathogenicity, frequency of occurrence and many others, 15-30 changes remain. Further we will analyze them in as much detail as possible,using additional databases and programs for determining pathogenicity, read articles, compare the patient's symptoms with those described in the literature. Only after this can we conclude which variant caused the disease,”Ryzhkova clarifies.
How hereditary diseases are discovered
If there is not enough data on the alleged culprit gene, then geneticists turn to genetic scientists for help. A team of researchers from the Laboratory of Functional Genomics of the Moscow State Scientific Center, simulating various variants of mutations in living organisms, proves or refutes hypotheses regarding the genes responsible for certain diseases.
During such research, scientists discover new genetic relationships.
“Every year we describe about a dozen new genes that are responsible for hereditary diseases. More recently, it was discovered that a mutation in the KIAA1019 gene causes fetal developmental disorders that are incompatible with life. A couple whose three pregnancies were terminated in the early stages came to the MGNC. We sequenced the fetal DNA and found new mutations in the completely unexplored KIAA1019 gene. Through experiments on cell lines, they proved that mutations found in parents lead to a complete breakdown of the KIAA1019 gene, which causes multiple malformations in the fetus. And when a mutation is known, it can be manipulated. In the next pregnancy, doctors carried out early prenatal diagnosis, the fetus turned out to be a carrier of a mutation in only one gene. This means that a completely healthy child will be born in this family. If the mutation came from both parentsthe pregnancy would have been terminated,”says Mikhail Skoblov, head of the functional genomics laboratory.
Skoblov is confident that the future of medical genetics is precisely in such prevention of hereditary genetic diseases. The patients themselves adhere to similar views. According to Irina Myasnikova, chairman of the All-Russian Society of Orphan Diseases, families with genetic problems should be able to conduct free pre-gestational and prenatal diagnostics.
“The cost of such diagnostics and the cost of therapy for patients with hereditary diseases are incomparable. This is beneficial for everyone: both the state, because there is no need to spend resources on therapy, and families, because they will have healthy children,”concludes Myasnikova.
Alfiya Enikeeva
