'Genes are to blame': what is heredity and what does it depend on
'08.09.2020'
Source: health.mail.ru
What is heredity? “I have bad genes,” - this phrase is often said without fully understanding its meaning, writes health.mail.ru.
In fact, the heredity of an organism is an extremely complex mechanism that is regulated by genetic, epigenetic ("supragenomic") factors and environmental conditions.
Even scientists and geneticists are still unable to finally figure out what affects heredity. However, some laws are still known to science.
What determines the "bad" heredity of a person
When doctors talk about genetic diseases, they mean monogenic diseases. This means that scientists were able to identify a specific gene, a mutation in which leads to the development of the disease. If a baby is born with an unsuccessful version of the gene, he will definitely get sick. In this case, a different combination of genes obtained from parents can be unsuccessful.
For some diseases, one "broken" copy is enough - this is what happens when inheritance is autosomal dominant. This is how, for example, Huntington's disease, Marfan's syndrome, type XNUMX neurofibromatosis are inherited.
In other situations, you need to get a mutant variant of the gene from both parents in order to get sick - this is an autosomal recessive inheritance. Thus, cystic fibrosis, phenylketonuria, sickle cell anemia, and non-syndromic hearing loss are inherited.
When a person receives only one unsuccessful copy of a gene in a disease that is transmitted through recessive inheritance, he does not get sick, but becomes a carrier. That is why two healthy people can have a child with a genetic disease - this is because mom and dad were carriers of the disease, and their child received from them two copies of the mutant gene.
In two healthy parents, the child can get sick if there is sex-linked inheritance. This means that the gene, the mutation in which provokes the development of the disease, is located on the sex chromosome. Among such diseases are hemophilia, Duchenne muscular dystrophy, color blindness.
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Why do expectant parents need a genetic test?
Most often, with sex-linked inheritance, women are healthy carriers, and their sons get sick. This is due to the fact that women have two X chromosomes, and the usual variant of a gene on one chromosome compensates for the presence of a "broken" version on the other.
Men, on the other hand, have only one X chromosome: if the child received from the mother exactly the chromosome with the mutant variant of the gene, he will get sick. Both hemophilia, color blindness, and Duchenne muscular dystrophy are caused by recessive gene mutations on the X chromosome, so the sons of female carriers get sick with them, while the mothers and their daughters remain healthy.
There are diseases in which different types of inheritance are possible. For example, spinal muscular atrophy (SMA) can be inherited in an autosomal dominant, autosomal recessive, and X-linked pattern.
“Of all the genetic diseases in my practice, I most often meet cystic fibrosis, phenylketonuria, SMA, non-syndromic hearing loss. Parents who carry mutant gene copies may be unaware that they are able to “reward” their child with a hereditary disease. Of course, not everyone can undergo a complete genetic screening - it is still quite expensive. But I advise the parents-to-be at least to take a test for the carriage of the most common mutations - it costs reasonable money and will help avoid big troubles with the child's health, ”says geneticist Irina Zhegulina.
The genetic association game
Most diseases do not have a clear inheritance - at least, scientists have not yet discovered it. But many diseases have hereditary factors that increase the risk of encountering them.
“In the case of hereditary predisposition, diseases do not have any specific genetic causes. And today's research is dedicated to finding genetic associations.
Let me give you an example. Scientists take a group of Europeans who have type XNUMX diabetes and a group of healthy Europeans. Then they study their genes and try to understand what mutations distinguish the healthy group from the sick group. It turns out a kind of averaged "genetic portrait" of a patient with type XNUMX diabetes. And if your genes are more like the genes of the sick than the genes of the healthy, then your risk of getting sick increases. But still, this does not mean that you will definitely get sick, ”explains Irina Zhegulina.
Most of the known genetic associations do not increase the risk of disease too much. But there are exceptions: for example, one mutation in the FLG gene, which is responsible for the skin protein filaggrin, increases the risk of atopic dermatitis by six times, two mutations as much as 150 times. A "breakdown" in the BRCA1 gene increases the risk of developing breast cancer from 12,4% to 55–65%.
Who puts "tags" on genes
“Usually a predisposition to a disease is a complex of genetic factors that together can lead to the development of a disease. Lifestyle is often the deciding factor - it can both exacerbate genetic risks and reduce them.
There are also epigenetic changes - a kind of “tags” on genes that change how they work. Epigenetic factors will also influence the risk of developing the disease.
But if scientists have more or less figured out genetics, then in the case of epigenetics, science is only taking the first steps in the study of its mechanisms. Why these “marks” appear, how do they affect genetic predispositions, whether they are inherited - all this is just for the doctors to find out, ”says Irina Zhegulina.
It is possible to suspect that heredity is to blame for the development of a common disease, if there are unusual reasons for its appearance or atypical development.
“Let's say a 50-year-old man comes to the doctor, he is obese, and he doesn't move much. The doctor discovers type XNUMX diabetes mellitus - most likely, the cause of the disease was lifestyle, and genetics had nothing to do with it. On the other hand, if an active young guy with an athletic physique comes to the doctor with signs of type XNUMX diabetes, he may have MODY diabetes, which is genetically determined, ”the doctor explains.
Hereditary traits
Color of eyes, hair, height, tendency to depression, temperament, resistance to stress - these and other signs and traits of character are also inherited only to a certain extent. Hereditary traits, like most diseases, are not a given, but a predisposition.
For example, if you do a genetic analysis, you can find out that you have "the probability of blue eyes - 72%, green - 27% and brown - 1%." What kind of eyes will actually turn out to be depends on the interaction of many genes. So school knowledge that the gene for brown eyes is dominant and the gene for blue eyes is recessive is not complete, everything is much more complicated. And if blue-eyed parents have a brown-eyed child, this is not a reason to file for divorce.
Eye color can be determined not only by the interaction of genes, but also by external factors. Reindeer, for example, have light eyes in summer - they reflect light well during the polar day. And in winter, the eyes turn blue - this allows animals to see better during the polar night. Obviously, in the genes of the deer, certain instructions are "sewn up" that allow you to change the color of the eyes depending on external conditions - this is an example of the bizarre interaction of heredity and the environment.
“Today, heredity is obvious only in terms of monogenic diseases. Everything else is still at the stage of study: scientists create biological databases, looking for associations between traits, diseases and genetic factors.
But so far, on most of the questions, science cannot give an answer for sure - is it heredity or not. So, geneticists, looking at the results of genetic tests, also cautiously draw conclusions about hereditary diseases, ”explains Irina Zhegulina.
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False "heredity"
An obese person can say: "Extra pounds is our family thing." And if you look at his relatives, it becomes clear why he says that: mom, dad, aunt and grandfather are all fat. But should bad heredity be immediately blamed?
Perhaps it's all about the lifestyle that is adopted in this family. If mom loves to cook potatoes with cracklings (and before her grandmother did this), parents help children get certificates for exemption from physical education (because they themselves hate sports), and the best rest is to lie on the couch, then it is not surprising that all family members have excess weight.
Although genetics can play a role - for example, if a mutation of the FTO gene is transmitted from generation to generation in this family, which slows down the feeling of satiety. However, healthy eating habits and rational food choices could solve this problem.
“At a consultation, a geneticist must ask a person in detail about his family history and habits. This will help to separate the real heredity from the “inherited” way of life, ”says Irina Zhegulina.
The doctor adds that today, with the help of genetics (combined with family and personal history), it is only possible to more accurately assess a person's individual risks. But in most cases it is impossible to say for sure whether he will get sick or not.
The material is published for educational purposes and is not a recommendation. ForumDaily Woman is not responsible for any diagnosis made by the reader based on the materials of the site, as well as for the consequences of self-medication, and may not share the point of view of the author or expert.
