Secrets of genetics: what children inherit from their parents. Genetic diseases that are inherited. Medical genetic examination

In ancient times, children who had various developmental disabilities were constantly mocked and ridiculed. In addition, people did not understand for what reasons such a child could be born. Only modern medicine gave an explanation for the origin of many diseases, although, unfortunately, they have not yet learned how to treat them.

Diseases transmitted through male line, are just as difficult to treat as other hereditary disorders. Doctors can only warn about wrong development fruit and offer to make a difficult choice.

Women who give birth to babies with autism or Down syndrome have previously been accused of evil spirit. They, as a rule, were burned, and the children were hunted down. Nowadays, genetics is seriously studying the problems of mankind and can explain why the fetus has certain developmental abnormalities.

It is already known that if both spouses have a certain set of genetic pathologies, the probability of having a “special” child is very high.

There are diseases that are transmitted only by female line. But also no less diseases are transmitted only through the male line. There are many types of such diseases. Unfortunately, not all of them have been studied to the end.

For example, more recently, doctors have identified a baldness gene that is transmitted through the male line. A large number of pathologies of the genital organs, also transmitted through the male line, and already mature men lead to infertility. In many cases, the deviation appears only after reaching a certain age.

It is to such severe hereditary diseases that hemophilia and schizophrenia belong.

Studies have shown that the risk of inheriting defects from a man is much higher than from a woman. In addition, fathers with birth defects are also more likely to have children with the same problems.

In general, boys with birth defects, rarely live to 20 years of age, because they have low interest survival.

Fortunately, the science of anthropogenetics provides answers to many questions that seem insoluble. She studies heredity. The part of anthropogenetics that studies diseases that are inherited belongs to medical genetics.

These two sciences are engaged in the study of small cells that contain information about our body. If nature lays it wrong, then a failure occurs.

Mutations (changes) occur at various levels. They are divided into gene, chromosomal and genomic. Most of these mutations lead to hereditary diseases. Gene mutations are the cause of impaired protein synthesis. About 1500 such diseases are already known to exist.

Among them, two groups are distinguished: molecular diseases, as well as metabolic diseases. About 600 metabolic diseases have been identified, which lead to a change in the carbohydrate, amino acid and lipid composition of the cell.

In particularly severe cases, these mutations can lead to malignant formations. Most of these mutations are inherited by children from their fathers.

heavy chronic disease, characterized by the appearance of numerous tumors of the nerve trunks, is neurofibromatosis. Children suffering from this disease lag behind in mental and physical development.

Another hereditary disease is phenylketonuria, accompanied by a sharp content of phenylatin (amino acids) in the blood. The products obtained from it are particularly toxic, which leads to mental retardation.

Galactosemia is a disease characterized by impaired carbohydrate metabolism. The body of a child suffering from galactosemia does not accept milk, and it should be transferred to dairy-free feeding as soon as possible. Otherwise, dementia and cirrhosis of the liver may develop.

Mucopolysaccharidosis is another disease transmitted through the male line. In this disease, the connective tissue suffers. Patients have a rather ugly physique and numerous defects of internal organs.

About 50 types of hereditary blood diseases arise as a result of molecular diseases. Many of these diseases are passed down through the male line.

Chromosomal diseases, which are associated with a violation of the number of chromosomes-autosomes, in most cases lead to the death of the child. And chromosomal diseases, which are associated with a violation of the sex chromosomes, cause changes in appearance, are characterized by the absence of secondary sexual characteristics and infertility.

In some cases, the fetus develops a genomic mutation. Newborns with this rare condition live only a few days. Mutation can be provoked by such unfavorable environmental factors as radiation, ultraviolet radiation, the action of chemical compounds, and on men who are more often exposed to stress, these factors are affected to a greater extent than on the fairer sex.

Why? After all, the Y chromosome of men is not symmetrical, unlike the X chromosome of women, so it “breaks”. For this reason genetic diseases through the male line and are transmitted more often than through the female.

Application in agriculture chemicals, experiments with radiation elements, as well as late visits to doctors, lead to the emergence of a whole range of harmful factors that can only provoke an increase in cases of transmission of hereditary diseases through the male line.

True reasons have not been identified so far. Science knows many theories about the factors that influence the appearance of this disease, triggers and predispositions. But the scientific world has not yet confirmed these theories with a 100% probability.

So, the most common theories of the origin of schizophrenia are:

• genetic theory. The essence of the theory is that it is inherited. As evidence for this theory, the facts are used that in families where parents suffer from schizophrenia, the disease appears more often than in others. A purely genetic theory is refuted by the fact of the disease of people in whose families cases of schizophrenia were not observed.
• dopamine theory. It is known that mental activity a person is dependent on the interaction and production of serotonin, dopamine, melatonin. It is scientifically known that in schizophrenia there is an increase in the stimulation of dopamine receptors. In contrast to this theory, the fact is stated that an increase in dopamine can cause delirium and, but this does not affect the will and emotions in any way, and therefore cannot cause schizophrenia.
• constitutional theory. She argues that the emergence and development of schizophrenia is influenced by the psychophysiological characteristics of a person.
• Infection theory. At present, this theory actually has no evidence base and is considered more from a historical point of view than from a practical one.
• neurogenetic theory. Science defines a situation of mismatch between the activity of the right and left hemispheres, due to a defect in the corpus callosum, which leads to the appearance of schizophrenia.
• Psychoanalytic theory. Psychoanalysis reveals the features of education in families of patients with schizophrenia. As a rule, in such families there is a lack of warm emotional relationships or the extreme opposite of the reactions of adults to the same actions of children.
• ecological theory. It is possible that the idea that poor ecology and malnutrition of the pregnant mother has a detrimental effect on the development of the fetus, causing predisposition to a number of diseases, and in particular to schizophrenia.
• evolutionary theory. high intelligence of a person has long been considered the norm, and not something outstanding, which is determined by the development of society as a whole. With the growth of intelligence, the features of the brain change, and the likelihood of schizophrenia increases.

It is generally accepted that schizophrenia, like many other mental illness, are caused by a combination of hereditary factors and circumstances of the external environment - human life. And yet, everyone is tormented by the question of whether schizophrenia can be inherited.

The figure of 1% characterizes schizophrenia very eloquently. It affects 1 out of 100 people. Absolutely every person has a risk of schizophrenia.

However, according to statistics, if your relatives in the first line had cases of schizophrenia, then the risk of this disease in you personally increases to 10%. If one of the second-line relatives (nephews, uncles, grandmothers, etc.) has schizophrenia, then the risk of the disease is determined from 2 to 6%. Most high risk schizophrenia, if the disease is diagnosed in identical twin. Scientists define it up to 40%.

And yet, in these statistics we are talking not about the hereditary transmission of the disease, but about the risk. By inheritance, a special structure of metabolic brain processes is transmitted. It is the metabolic processes in the brain during certain conditions, cause splitting, defined as schizophrenia.

The gene for schizophrenia is periodically “found” different groups research scientists, but repeated and subsequent studies do not confirm these theories. Human genes are located on 23 pairs of chromosomes. By inheritance, a person receives 2 copies of each chromosome: from mom and from dad. Several genes are associated with the risk of the disease, but none of them directly causes schizophrenia. Therefore, based on genetic analysis It is impossible to predict the likelihood of a person developing schizophrenia.

This means that the gene for schizophrenia does not exist or it has not been found at the present time. However, it cannot be said that schizophrenia is not related to heredity. With a combination of such components as heredity and adverse environmental factors, the risk of schizophrenia increases several times.

Adverse factors are: viral diseases, trauma during childbirth, malnutrition mothers during pregnancy, traumatic factors.

For the appearance of schizophrenia, in addition to the initial characteristics, so-called triggering mechanisms are needed.

Such mechanisms can be:

• drugs;
• alcohol;
• stressful situations;
• psychological trauma;
• unfavorable environmental conditions.

Schizophrenia can appear at any age, depending on the triggering conditions, but is most common in crisis periods: senior preschool, junior school, teenage, youthful, midlife crisis, pension. As you can see, listed age periods associated with critical characteristics.

To predict the likelihood of a disease in a person, you need to pay attention to the age at which schizophrenia appeared in relatives. It is possible that there is an observation of the same periods of development of the disease.

Is schizophrenia transmitted through the male line?

Everything described above, including the triggering mechanisms and genetics of the disease, applies equally to men and women, without prioritizing any of the sexes.

However, there is an opinion that schizophrenia is transmitted through the male line. What is this theory based on?

1. The genetic predisposition to the disease is equally transmitted through the male and female lines. However, the manifestation of schizophrenia in men, as a rule, is brighter and more noticeable than in women. Therefore, men with schizophrenia are more visible to relatives than women. Therefore, the risk of the disease is associated with the male line.
2. Triggers are a number of factors, including alcohol, drugs. Statistics show that alcoholism is still considered to be a predominantly male problem, although the percentage of male alcoholics and drug addicts is slightly higher than that of women. It is this reason that shows more cases of schizophrenia among the male population.
3. Stress and mental complications during periods age crises experienced by men deeper and stronger. Given the genetic condition of the risk of schizophrenia, the triggering of these mechanisms is most likely in men.
4. Raising boys is often tougher than raising girls. Parents do not allow the manifestation of gentleness, which affects emotional development child.

The fact that the health of the population, and especially men, is getting worse is no secret. Medical statistics state the growth of schizophrenia and its rejuvenation.

There are a few months left before meeting with the baby, and you can’t wait to find out who he will look like: his blue-eyed, fair-haired dad or dark brown-eyed mom? What if he "gets" the famous grandfather's nose or all the grandmother's moles?! You will get the answer to these questions on the baby’s birthday, because our appearance depends on the random distribution of the genes of our parents. True, this lottery still has its own laws.

The story of any of us begins with the meeting of the egg and sperm. Each of these cells has its own luggage of 23 chromosomes, from the fusion of which a unique creature with a set of 46 chromosomes appears. Each of them resembles a necklace a meter long, and only a few billionths of a millimeter wide - experts call it DNA, or deoxyribonucleic acid. This necklace consists of hundreds of "pearls" - genes. They encoded our physical characteristics: blue or Brown eyes, thin or plump lips, low or average height. It's just impossible to predict which genes a child will inherit! Judge for yourself: the egg contains only half of the mother's genetic "capital" - 23 of the 46 chromosomes that she owns. The same thing happens with the "luggage" of the future dad. In such confusion, it is impossible to predict where the gene will end up. curly hair and the gene for blue eyes, will they fall into the part that the child received, or will they be left out? Moreover, the first round of the lottery will be followed by the second one! After the meeting, the genes are crossed - this is how new qualities appear. For each of their physical traits the baby receives two genes: one from the father, the other from the mother. These genes can either carry the same information (“blue” for eye color, “straight” for hair, “humped” for nose), or different (“blue” and “brown”, “straight” and “curly”, “humped” and "smooth"). In the first case, there is no problem: a child with two "blue" genes will have blue eyes. But if they are different - "blue" and "brown" - that gene that is stronger will win!

WHO WILL WIN?

Our genes have different properties: those that prevail and necessarily appear are called dominant, and those that are “silent” are called recessive. The former are usually responsible for more dark colors And characteristics. They can suppress the action of genes responsible for light colors and neutral traits. For example, we can safely assume that the combination of a dark-haired dad with a hooked nose and a blonde mom with a straight, even profile will be dominated by the characteristics of the father. And yet this confident assumption does not mean that it will be so. After all, it is thanks to the variety of possible combinations of genes that your child will be unique in the truest sense of the word. Let's see how inheritance laws work in different situations.

I dream of a girl blue eyes like my husband has. Is there any hope for me if I myself am the owner of brown eyes?

The blue eye gene is recessive. In other words, in order to manifest itself, it must be present in the baby's chromosome set in duplicate: one from dad, the other from mom. Your husband has blue eyes, which means that both genes responsible for their color are “blue” in his “luggage”. But do you have such a gene? If the dominant gene “brown eyes” appeared in your set, this does not mean that you do not have one more, hidden for the time being, “blue”. So, the first hypothesis: you have both genes "brown". Then everything is decided: your "brown" will win the "blue" husband.

The second hypothesis: you are a carrier of a hidden "blue" gene. In this case, there is a chance to give birth to a girl with blue eyes.

We have only girls in our family. Does that mean that I'm like future mother no choice?

It is known that spermatozoa with the Y chromosome are more mobile than their X counterparts, but they do not live long. This means that conception close to the time of ovulation is likely to give birth to a boy. If you made love 3-4 days before or after ovulation, you are more likely to give birth to a girl.

We are both musicians. Will the child inherit our abilities?

The controversy about congenital and acquired has been going on for a long time. The researchers were able to establish that the auditory cortex of musicians (the so-called part of the brain that processes sounds) is better developed than that of other people. But this fact does not explain anything. Does a person become a musician because he inherits a developed auditory cortex? Or does the auditory cortex develop because of an addiction to music? And although specialists do not have an exact answer to these questions today, they consider it proven that not all human traits are inherited and our brain is influenced environment. This means that life in a family of musicians can instill in a child a love of music!

I am small and my husband is tall. Does this mean that our child will be of average height?

Of course, the genes we receive affect our growth. It is clear that the parents vertically challenged the child, most likely, will be short, for tall ones - on the contrary. But a combination of opposite signs can give an unpredictable result: either the baby will inherit the data of the mother or father, or “turn out” somewhere in the middle. It's impossible to guess! Meanwhile, do not forget that each new generation is higher than the previous one - this feature is associated with a change in our diet.

Is it possible to know in advance the blood type of a child?

It is rather difficult to do this. One can only be sure that parents with blood group IV (AB) cannot have a child with group I (O). And the owners of group I (O) will definitely have a baby with the same “indicator”. In all other situations, nothing definite can be said. For example, a mother with group I (O) and a father with group IV (AB) may have a baby with group II (OA) or III (OB). Experts also determined the relationship of blood groups among themselves: I (O) - recessive in relation to II (OA) and III (OB).

My husband and I have plump lips. Can our baby be thin-lipped?

Yes, if both of you are carriers of the recessive gene " thin lips and both of these genes will meet. By joining their "efforts", they will reveal a feature that until now was hidden.

One of my cousins suffering from Down's disease. Does this mean that our family has such a gene?

Down syndrome is not a hereditary disease, it is caused by an error in cell division. In this case, the egg (in 90% of cases) or sperm (10% of cases) turns out to be a carrier of two chromosomes 21 instead of one - and the child receives three such samples instead of two. I must say that the risk of transferring an extra chromosome increases with age. If among 20-year-old expectant mothers this happens in 1 case out of 2000, then for 40-year-olds it happens in 1 out of 100. Fortunately, modern ways diagnostics make it possible to determine Down's disease, starting from the first trimester of pregnancy using a chorionic biopsy (the so-called study of the tissues of the future placenta) at 10-12 weeks of pregnancy, amniocentesis (analysis amniotic fluid) at 16-20 weeks, cordocentesis (analysis of umbilical cord blood) at 20-24 weeks. The reason for examining the expectant mother is her age (from 35 years old), changes in the level of "serum markers" in the blood, the results of ultrasound, or rather, the thickening of the baby's collar zone.

My sister has a child with cystic fibrosis. Should I be worried or not?

If your family has cases of the development of genetic diseases, then before planning a pregnancy, you need to turn to genetics.

Cystic fibrosis most often occurs unexpectedly, that is, there are no such patients in the father's family or in the mother's family. This circumstance is explained by the fact that cystic fibrosis is a recessive disease, that is, a person can be a carrier of an "altered" gene and not know about it. Such a person is called a "healthy carrier".

Unfortunately, if either parent passes the broken gene on to the child, the child will develop cystic fibrosis. In a situation where both parents are healthy carriers, the risk of having a sick child is 25%, however, as well as a healthy one; in the remaining 50%, the baby will be a healthy carrier, like mom and dad. If the father of the child is a healthy carrier of the “altered” gene, and the mother does not have it at all, the baby will “go” either to the father or to the mother.

There are several cases of color blindness in my family. Is this trait inherited?

Color blindness is a genetic “breakdown” carried by the X chromosome. Contrary to popular belief, color blind people do not confuse green and orange, but perceive both colors as gray. There are many more color blind boys (8%) than girls (0.5%). This fact is explained by the fact that they have two X chromosomes, which means that if the baby receives a broken chromosome from one of the parents, the second, “healthy”, will compensate for it. Boys - carriers of one X and one Y chromosome - do not have a duplicate to correct the anomaly.

We have a mixed, Afro-European couple. What color will our children's skin be?

Any option is possible: from the lightest to the darkest. The fact is that skin color is encoded not in one, but in several genes. Usually, the mixture of signs of African and Caucasian races gives the child's skin a shade of coffee with milk. Although the final result also depends on the genealogy of the parents. If the child's father is an African in several generations, the baby's skin color will be darker, but if he is mulatto, the child will "turn out" fair.

I have always been full. Will my child have weight problems?

The baby may inherit a predisposition to be overweight, but even in this case, his weight will depend on many circumstances, including nutrition. In addition, in order to answer your question, you need to take into account the heredity and physique of the future dad.

Scientists believe that intellectual ability 50–70% are determined by genes, and the choice of profession is 40%. At 34%, we have a tendency to be polite and rude. Even the desire to sit in front of the TV for a long time is 45% a genetic predisposition. The rest, according to experts, is determined by education, social environment and sudden blows of fate - for example, diseases.

A gene, just like an individual organism, is subject to natural selection. If, for example, it allows a person to survive under more severe climatic conditions or longer hold physical exercise- it will spread. If, on the contrary, it provides the appearance of some harmful trait, then the prevalence of such a gene in the population will fall.

During prenatal development child, this influence of natural selection on individual genes can manifest itself in a rather strange way. For example, genes inherited from the father are "interested" in rapid growth fetus - since the father's body obviously does not lose from this, and the child grows faster. Maternal genes, on the other hand, promote slower development—which ends up taking longer, but leaving the mother with more energy.

Prader-Willi syndrome is an example of what happens when mom's genes "win". During pregnancy, the fetus is inactive; after birth, the child has a developmental delay, a tendency to obesity, short stature, drowsiness and incoordination. It may seem strange that these apparently unfavorable traits are encoded by maternal genes - but it must be remembered that normally the same genes compete with paternal ones.

In turn, the “victory” of paternal genes leads to the development of another disease: Angelman syndrome. In this case, the child develops hyperactivity, often epilepsy and delayed speech development. Sometimes lexicon the patient is limited to just a few words, and even in this case, the child understands most of what is said to him - it is the ability to express his thoughts that suffers.

Of course, it is impossible to predict the appearance of the child. But you can say with a certain degree of certainty what the main features will be. Dominant (strong) and recessive (weak) genes will help us with this.

For each of its external and internal signs the child receives two genes. These genes can match ( high growth, plump lips) or different (high and low, plump and thin). If the genes match, there will be no conflict, and the child inherits full lips and tall stature. Otherwise, the strongest gene wins.

A strong gene is called dominant, and a weak gene is called recessive. The composition of strong genes in humans includes dark and curly hair; baldness in men; brown, or green eyes; normally pigmented skin. Recessive traits include blue eyes, straight, blond or red hair, and lack of skin pigment.

When a strong and a weak gene meet, the strong one usually wins. For example, mom is brown-eyed brunette, and dad is blond with blue eyes, with a high degree of probability we can say that the baby will be born with dark hair and brown eyes.

True, brown-eyed parents may have a newborn with blue eyes. Thus, the genes received from the grandmother or the grandfather could affect. The opposite situation is also possible. The explanation is that it turns out that not one gene from each parent, as was previously believed, is responsible for any trait, but a whole group of genes. And sometimes one gene is responsible for several functions at once. So a number of genes are responsible for the color of the eyes, which each time are combined in a different way.

Hereditary diseases transmitted by genes

A baby can inherit from his parents not only appearance and character traits, but also diseases (cardiovascular, oncological, diabetes, Alzheimer's and Parkinson's).

The disease may not manifest itself if elementary safety measures are taken. Tell your gynecologist in detail about serious violations health not only yours with the husband, but also close relatives. This will help protect the baby in the future. Sometimes absolutely healthy parents a baby is born with a hereditary disease. It was laid down in the genes and manifested itself only in the child. This usually happens when both parents have the same disease in their genes. Therefore, if a child is planned, according to experts, it is better to undergo a genetic examination. This is especially true of a family in which children with hereditary diseases were already born.

A weak gene may not be detected in one or many generations until two recessive genes from each parent meet. And then, for example, such a rare sign as albinism may appear.

Chromosomes are also responsible for the sex of the child. For a woman, the chances of giving birth to a girl or a boy are equal. The sex of the child depends only on the father. If an egg meets a sperm with an X sex chromosome, it will be a girl. If U - a boy will be born.

What else can depend on genes:

Gender - 100%;

Height - 80% (for men) and 70% (for women);

Blood pressure - 45%;

Snoring - 42%;

Female infidelity - 41%;

Spirituality - 40%;

Religiosity - 10%.

There are also genes responsible for the development of certain conditions, such as depression or a tendency to uncontrolled eating.

The level of mutations in men is 2 times higher than in women. Thus, it turns out that humanity owes its progress to men.

All representatives of the human race are 99.9% identical in DNA, which completely sweeps aside any basis for racism.

In countries where the system of early detection of dementia is developed, every fourth person over the age of 55 has a close relative with this diagnosis. Therefore, the question of the hereditary nature of dementia is very relevant today. This is one of the most common questions that caring relatives ask the doctor. Anyone who has encountered this disease in their family is interested in whether it can be inherited and what is the probability of transmission from parents to children.

Genetics is one of the most rapidly developing sciences of the 21st century. Therefore, every year scientists are moving further and further in obtaining an answer to this question. Experts confirm that genes - DNA fragments through which parents pass on hereditary traits to their children - can play a significant role in the development of dementia, but emphasize that in most cases the effect of genes is not direct, but indirect. In fact, hereditary predisposition is only part of a motley mosaic of dozens of factors leading to the development of impaired memory and thinking. They can ask increased likelihood launching negative processes, however, parallel correction of other factors (for example, a healthy lifestyle: physical activity, rational nutrition, rejection bad habits) can neutralize this effect. But first things first.

What is a gene?

Genes are fragments of DNA that contain instructions for our body: how it should develop and how to maintain its existence. Such instructions can be found in almost every cell in our body. Usually each person carries two copies of each gene (from the mother and from the father), packed into paired structures - chromosomes.

Modern science has about 20,000 genes. In general, the genes of all people are similar, and therefore our bodies are arranged in approximately the same way and work in a similar way. At the same time, each organism is unique, and genes are also responsible for this, or rather, the slight differences that can be found between them.

The differences are of two kinds. The first type is called variation. Variants are varieties of genes that do not contain defects or other anomalies. They differ in some nuances that play a role in how our body works, but do not lead to pathological deviations in this work. The probability of developing a particular disease may depend on them, but their influence is not decisive. The second kind is called a mutation. The impact of the mutation is more significant and can be harmful to the body. In some cases, a particular characteristic of an organism can be caused by a mutation in a single gene. An example of this is Huntington's disease. A person who inherits a mutated version of the gene responsible for Huntington's disease is doomed to develop this disease at a certain age.

Both paths can lead to dementia.

Very rarely there are cases of direct inheritance of a gene mutation leading to the development of dementia. More often the disease is determined complex combination hereditary factors among themselves and with the conditions of the environment / lifestyle of a person. One way or another, the gene factor always plays a role in dementia of any origin. There are genetic variants that influence our predisposition to cardiovascular diseases or to metabolic disorders, and through this indirectly increase the risk of developing dementia. However, these predispositions may not manifest themselves if their carrier leads a healthy lifestyle and is not exposed to negative impact external environment.

Contrary to popular belief, the influence of genes on the development of dementia is not decisive.

Now, from general words, let's turn to the most common causes of dementia and see how each of them is related to heredity. Causes include Alzheimer's disease, cerebral circulation, diffuse Lewy body disease, and lobar frontotemporal degeneration.

Alzheimer's disease

Apparently, the genetics of Alzheimer's disease, the most common cause of dementia, is currently the most thoroughly studied. Predisposition to this disease can be inherited in both ways: monogenic (through a single mutated gene) or polygenic (through a complex combination of variants).

Familial form of Alzheimer's disease

Cases of a monogenic variant of Alzheimer's disease are very rare. Today, there are less than a thousand families in the world in which the disease is transmitted from parents to children. If one of the parents is a carrier of the mutated gene, each of his children will have a 50% chance of inheriting this gene. In this case external symptoms Alzheimer's disease, as a rule, begins to develop quite early: already after 30 years (recall that non-hereditary forms usually make themselves felt no earlier than 65 years).

The familial form of Alzheimer's disease is usually associated with a mutation in one of three genes: the amyloid precursor protein (APP) gene and two presenilin genes (PSEN-1 and PSEN-2). Of these three, the most common (approximately 80% of all reported cases) is a presenilin-1 gene mutation on chromosome 14 (more than 450 families). Symptoms in this case appear already at the age of 30 years. The second most common mutation is in the APP gene on chromosome 21 (about 100 families). This mutation directly affects the production of beta-amyloid, a protein whose deposits scientists believe to be a major factor in the development of Alzheimer's disease. About 30 families worldwide have a mutation in the PSEN-2 gene on chromosome 1, causing familial Alzheimer's disease, which may begin later than for PSEN-1.

There are two points to note here. First, scientists may not be aware of all cases family options Alzheimer's disease due to the fact that there are still many corners of the world where science and the health care system are underdeveloped. Secondly, in several families with clear signs family form Alzheimer's disease, none of these mutations was found, which suggests the existence of other mutations not yet known to scientists. Thirdly, even when Alzheimer's disease begins very early, at the age of 30, it may not be a form with a family pattern of inheritance. For this age, the probability of a familial form is approximately 10%, while on average, the familial form accounts for less than 1%.

Genes that increase the risk of developing Alzheimer's disease

The vast majority of people with Alzheimer's disease inherit it from their parents in a very different way - through a complex combination of different variants of many genes. This can be figuratively compared with bizarre patterns in a kaleidoscope, with each turn appears new drawing. Therefore, the disease can skip a generation, or appear as if from nowhere, or not be transmitted at all.

Currently, scientists have identified more than 20 gene variants (or DNA fragments) that, to one degree or another, affect the chances of getting Alzheimer's disease. Unlike mutated genes in the familial form, all of these variants do not rigidly cause the development of Alzheimer's disease, but only slightly increase or decrease the risk. Everything will depend on their interaction with other genes, as well as with factors such as age, environmental conditions, lifestyle. As already noted, the polygenic form usually manifests itself already in old age, after 65 years.

The best known and most studied gene that increases the risk of developing Alzheimer's disease is called apolipoprotein E (APOE). This gene is found on chromosome 19. The eponymous APOE protein plays a role in the processing of fats in the body, including cholesterol. The APOE gene exists in three variants, denoted by the Greek letter epsilon (e): APOE e2, APOE e3, and APOE e4. Since each of us is a carrier of a pair of APOE genes, there are six possible different combinations: e2/e2, e2/e3, e3/e3, e2/e4, e3/e4 ​​or e4/e4. The risk depends on which combination fell to us.

The most unfavorable option is the carriage of two variants of APOE e4 at once (one from each parent). Scientists believe that this combination occurs in approximately 2% of the world's population. The increase in risk is about 4 times (according to some sources - 12), but believe me - this is far from a 100% probability. For those who inherited only one copy of e4 in combination with another variant (about a quarter of all people), the risk of developing Alzheimer's disease increases by about 2 times. The first symptoms in carriers of the e4 gene may appear before the age of 65.

The most common combination is two e3 genes (60% of all people). In this case, scientists estimate the risk as medium. Approximately one in four carriers of this combination will suffer from Alzheimer's disease if they live to be 80 years old.

Carriers of the e2 variant have the lowest risk (11% inherit one copy and only half a percent inherit two.

Data for Russia became known recently, after the publication of the results of a study conducted by the medical genetic center Genotek. For the study, the results of DNA tests conducted from November 1, 2016 to July 1, 2017 were used for men and women aged 18 to 60 years (the total number of studies was 2.5 thousand). Thus, 75% of Russians had a neutral e3/e3 genotype, which is not associated with an increased or decreased risk of developing Alzheimer's disease. 20% of Russians have the e3 / e4 and e2 / e4 genotypes of the APOE gene, which increase the likelihood of developing the disease by five times, and 3% of Russians have the e4 / e4 genotype, which increases this probability by 12 times. Finally, the e2/e2 genotype, associated with a reduced risk of developing Alzheimer's disease, was found in 2% of the lucky ones.

For a long time, scientists did not associate the likelihood of developing Alzheimer's disease with a late onset with any other genes, except for APOE. However, in last years Thanks to the rapid development of genetics, several more genes have been discovered whose variants are associated with an increased or decreased risk of developing Alzheimer's disease. Their influence on the development of Alzheimer's disease is even lower than that of APOE, and their names will not say anything to a wide audience, but we will list them anyway: CLU, CR1, PICALM, BIN1, ABCA7, MS4A, CD33, EPHA1 and CD2AP. They play a role in the wearer's tendency to develop inflammation, problems immune system, fat metabolism, and through this affect the chances of developing symptoms of Alzheimer's disease. The researchers themselves believe that this list can be significantly expanded in the future.

Thus, if one of your family members (grandfather, grandmother, father, mother, brother or sister) has been diagnosed with late-onset Alzheimer's disease, you are slightly more likely to develop the disease than someone with no family history of Alzheimer's disease. Increased overall risk in this case insignificant, and it can be compensated in a healthy way life. The risk is slightly higher when both parents have Alzheimer's disease. In this case, the risk of developing Alzheimer's disease after age 70 would be approximately 40% (Jayadev et al. 2008).

Vascular dementia

Cerebral circulation disorders are the second most common cause of dementia.

Familial vascular dementia

As with Alzheimer's disease, vascular dementia caused by a gene mutation is extremely rare. These include, for example, autosomal dominant cerebral arteriopathy with subcortical infarcts and leukoencephalopathy, which occurs when a mutation occurs in a gene called NOTCH3.

Genes that increase the risk of developing vascular dementia

First, some studies have shown that modification of the APOE e4 gene may increase the risk of developing vascular dementia, but this risk is lower than for Alzheimer's disease. Whether carrying APOE e2 lowers the risk is not yet clear.

Secondly, scientists have identified several genes that influence the patient's tendency to high cholesterol, elevated blood pressure or type 2 diabetes. Each of these conditions can be a factor in the development of mucosal dementia in old age. A family history of stroke or heart disease can also increase the risk, but in general, genes play a much smaller role in the development of vascular dementia than in the development of Alzheimer's disease. For dementia associated with cerebrovascular accident, more important role lifestyle plays: in particular diet and exercise.

Frontotemporal dementia (FTD)

In the genesis of frontotemporal dementia - especially its behavioral form (less often semantic) - genes play the most prominent role.

Familial frontotemporal dementia

About 10-15% of people with FTD have severe family history- the presence of at least three relatives with a similar disease in the next two generations. About the same number (about 15%) have a less pronounced history, perhaps even with a different type of dementia. About 30% of all cases of FTD are due to a mutation in a single gene, and at least eight such genes are known, including very rare mutations.

Three mutated genes are the most common cause of FTD: C9ORF72, MAPT, and GRN. There are certain differences in how they manifest themselves. For example, C9ORF72 causes not only FTD, but also motor neuron disease.

As in familial cases of Alzheimer's disease, the probability of inheriting a defective gene from one of the parents is 50%, and in the case of inheritance, the probability of developing the disease is 100% (the exception is the C9ORF72 gene, for reasons that are not clear to science, the disease does not always develop when it is inherited) .

Genes that increase the risk of developing FTD

Although the main attention of scientists is focused on monogenic cases of FTD, in recent years there has been a search for polygenic variants. In particular, a gene called TMEM106B was discovered, whose variants indirectly affect the likelihood of developing the disease.

Dementia with Lewy bodies

The genetics of Lewy body dementia (LBD) is one of the least studied topics. Some authors of the few studies cautiously suggest that the presence of a patient with LTD among the next of kin may slightly increase the risk of developing this type of dementia, but it is too early to draw final conclusions.

Familial cases of dementia with Lewy bodies

Such cases are known to science. In several families, a rigid inheritance pattern has been identified, but the mutation of the gene responsible for this pattern has not yet been identified.

Genes that increase the risk of developing LTD

The APOE e4 variant is thought to be the strongest genetic risk factor for LTD, as it is for Alzheimer's disease. Variants of two other genes, glucocerebrosidase (GBA) and alpha-synuclein (SNCA), also affect the risk of developing LBD. Alpha-synuclein is the main protein in Lewy bodies. The GBA and SNCA genes are also risk factors for Parkinson's disease. Diffuse Lewy body disease, Alzheimer's disease and Parkinson's disease have common features - both in terms of pathological processes as well as in terms of symptoms.

Other reasons

Less common causes of dementia with a strong genetic component include Down's syndrome and Huntington's disease.

Huntington's disease refers to an inherited disease caused by a mutation in the HTT gene on chromosome 4. Symptoms of Huntington's disease include cognitive impairment that can reach the degree of dementia.

Approximately one in two people with Down syndrome who lives to age 60 develops Alzheimer's disease. Increased Risk due to the fact that most patients have an extra copy of chromosome 21, which means an extra copy of the amyloid precursor protein gene located on this chromosome. This gene is associated with the risk of developing Alzheimer's disease.

Is genetic testing worth it?

Most doctors do not recommend. If we talk about polygenic inheritance (as the most common), then of all the genes, only APOE ε 4 significantly increases the risk of developing dementia (up to 15 times in the homozygous variant), but even if you are very unlucky and this particular variant is identified, the prediction accuracy will be too far from 100%. The opposite is also true: if the gene is not found, this does not guarantee against the development of the disease. Testing, therefore, does not allow making predictions with the required level of certainty.