Gene mutations: causes, examples, classification. Gene mutations

Mutations at the gene level are molecular structural changes in DNA that are not visible in a light microscope. These include any transformation of deoxyribonucleic acid, regardless of their impact on viability and localization. Some types of gene mutations do not have any effect on the function and structure of the corresponding polypeptide (protein). However, most of these transformations provoke the synthesis of a defective compound that has lost its ability to perform its tasks. Next, we consider gene and chromosomal mutations in more detail.

Characteristics of transformations

The most common pathologies that provoke human gene mutations are neurofibromatosis, adrenogenital syndrome, cystic fibrosis, phenylketonuria. This list can also include hemochromatosis, Duchenne-Becker myopathy and others. These are not all examples of gene mutations. Their clinical signs are usually metabolic disorders (metabolic process). Gene mutations can be:

Change in the base codon. This phenomenon is called a missense mutation. In this case, a nucleotide is replaced in the coding part, which, in turn, leads to a change in the amino acid in the protein.
Changing the codon in such a way that the reading of information is suspended. This process is called nonsense mutation. When a nucleotide is replaced in this case, a stop codon is formed and translation is terminated.
Reading error, frame shift. This process is called "frameshift". With a molecular change in DNA, triplets are transformed during the translation of the polypeptide chain.

Classification

According to the type of molecular transformation, the following gene mutations exist:

duplication. In this case, repeated duplication or duplication of a DNA fragment from 1 nucleotide to genes occurs.
deletion. In this case, there is a loss of a DNA fragment from a nucleotide to a gene.
Inversion. In this case, a 180 degree turn is noted. section of DNA. Its size can be either two nucleotides or a whole fragment consisting of several genes.
Insertion. In this case, DNA segments are inserted from the nucleotide to the gene.

Molecular transformations involving from 1 to several units are considered as point changes.

Distinctive features

Gene mutations have a number of features. First of all, it should be noted their ability to be inherited. In addition, mutations can provoke the transformation of genetic information. Some of the changes can be classified as so-called neutral. Such gene mutations do not provoke any disturbances in the phenotype. So, due to the innate nature of the code, the same amino acid can be encoded by two triplets that differ in only 1 base. However, a certain gene can mutate (transform) into several different states. It is this kind of change that provokes most of the hereditary pathologies. If we give examples of gene mutations, then we can refer to blood groups. So, the element that controls their AB0 system has three alleles: B, A and 0. Their combination determines blood groups. Relating to the AB0 system, it is considered a classic manifestation of the transformation of normal signs in humans.

Genomic transformations

These transformations have their own classification. The category of genomic mutations includes changes in the ploidy of structurally unaltered chromosomes and aneuploidy. Such transformations are determined by special methods. Aneuploidy is a change (increase - trisomy, decrease - monosomy) in the number of chromosomes of the diploid set, not multiple of the haploid one. With a multiple increase in the number, they speak of polyploidy. These and most aneuploidies in humans are considered lethal changes. Among the most common genomic mutations are:

Monosomy. In this case, only one of the 2 homologous chromosomes is present. Against the background of such a transformation, healthy embryonic development is impossible for any of the autosomes. Monosomy on the X chromosome is the only one compatible with life. It provokes the Shereshevsky-Turner syndrome.
Trisomy. In this case, three homologous elements are revealed in the karyotype. Examples of such gene mutations: Down syndrome, Edwards, Patau.

Provoking factor

The reason why aneuploidy develops is considered to be the non-disjunction of chromosomes during cell division against the background of the formation of germ cells or the loss of elements due to anaphase lag, while when moving towards the pole, the homologous link may lag behind the non-homologous one. The concept of "nondisjunction" indicates the absence of separation of chromatids or chromosomes in mitosis or meiosis. This disruption can lead to mosaicism. In this case, one cell line will be normal and the other monosomic.

Nondisjunction in meiosis

This phenomenon is considered the most frequent. Those chromosomes that should normally divide during meiosis remain connected. In anaphase, they move to one cell pole. As a result, 2 gametes are formed. One of them has an extra chromosome, while the other lacks an element. In the process of fertilization of a normal cell with an extra link, trisomy develops, gametes with a missing component - monosomy. When a monosomic zygote is formed for some autosomal element, development stops at the initial stages.

Chromosomal mutations

These transformations are structural changes in the elements. As a rule, they are visualized in a light microscope. Chromosomal mutations usually involve tens to hundreds of genes. This provokes changes in the normal diploid set. As a rule, such aberrations do not cause sequence transformation in DNA. However, when the number of gene copies changes, a genetic imbalance develops due to a lack or excess of material. There are two broad categories of these transformations. In particular, intra- and interchromosomal mutations are distinguished.

Environmental influence

Humans have evolved as groups of isolated populations. They lived long enough in the same environmental conditions. We are talking, in particular, about the nature of nutrition, climatic and geographical characteristics, cultural traditions, pathogens, and so on. All this led to the fixation of combinations of alleles specific for each population, which were the most appropriate for living conditions. However, due to the intensive expansion of the range, migrations, and resettlement, situations began to arise when useful combinations of certain genes that were in one environment in another ceased to ensure the normal functioning of a number of body systems. In this regard, part of the hereditary variability is determined by an unfavorable complex of non-pathological elements. Thus, changes in the external environment and living conditions act as the cause of gene mutations in this case. This, in turn, became the basis for the development of a number of hereditary diseases.

Natural selection

Over time, evolution proceeded in more specific forms. It also contributed to the expansion of hereditary diversity. So, those signs were preserved that could disappear in animals, and vice versa, what remained in animals was swept aside. In the course of natural selection, people also acquired undesirable traits that were directly related to diseases. For example, in humans, in the process of development, genes have appeared that can determine sensitivity to polio or diphtheria toxin. Having become Homo sapiens, the biological species of people in some way "paid for its rationality" by accumulation and pathological transformations. This provision is considered the basis of one of the basic concepts of the doctrine of gene mutations.

Gene mutations - a change in the structure of one gene. This is a change in the sequence of nucleotides: dropout, insertion, replacement, etc. For example, replacing a with m. Causes - violations during doubling (replication) of DNA

Gene mutations are molecular changes in the structure of DNA that are not visible under a light microscope. Gene mutations include any changes in the molecular structure of DNA, regardless of their location and impact on viability. Some mutations have no effect on the structure and function of the corresponding protein. Another (most) part of gene mutations leads to the synthesis of a defective protein that is unable to perform its proper function. It is gene mutations that determine the development of most hereditary forms of pathology.

The most common monogenic diseases in humans are: cystic fibrosis, hemochromatosis, adrenogenital syndrome, phenylketonuria, neurofibromatosis, Duchenne-Becker myopathies and a number of other diseases. Clinically, they are manifested by signs of metabolic disorders (metabolism) in the body. The mutation may be:

1) in a base substitution in a codon, this is the so-called missense mutation(from English, mis - false, incorrect + lat. sensus - meaning) - a nucleotide substitution in the coding part of the gene, leading to an amino acid substitution in the polypeptide;

2) in such a change in codons, which will lead to a stop in reading information, this is the so-called nonsense mutation(from Latin non - no + sensus - meaning) - a nucleotide replacement in the coding part of the gene leads to the formation of a terminator codon (stop codon) and the termination of translation;

3) a violation of reading information, a shift in the reading frame, called frameshift(from the English frame - frame + shift: - shift, movement), when molecular changes in DNA lead to a change in triplets during the translation of the polypeptide chain.

Other types of gene mutations are also known. According to the type of molecular changes, there are:

division(from lat. deletio - destruction), when there is a loss of a DNA segment ranging in size from one nucleotide to a gene;

duplications(from lat. duplicatio - doubling), i.e. duplication or re-duplication of a DNA segment from one nucleotide to entire genes;

inversions(from lat. inversio - turning over), i.e. a 180° turn of a DNA segment ranging in size from two nucpeotides to a fragment that includes several genes;

insertions(from lat. insertio - attachment), i.e. insertion of DNA fragments ranging in size from one nucleotide to the whole gene.

Molecular changes affecting one to several nucleotides are considered as point mutations.

Fundamental and distinctive for a gene mutation is that it 1) leads to a change in genetic information, 2) can be transmitted from generation to generation.

A certain part of gene mutations can be classified as neutral mutations, since they do not lead to any changes in the phenotype. For example, due to the degeneracy of the genetic code, the same amino acid can be encoded by two triplets that differ only in one base. On the other hand, the same gene can change (mutate) into several different states.

For example, the gene that controls the blood group of the AB0 system. has three alleles: 0, A and B, combinations of which determine 4 blood groups. The AB0 blood group is a classic example of the genetic variability of normal human traits.

It is gene mutations that determine the development of most of the hereditary forms of pathology. Diseases caused by such mutations are called gene, or monogenic, diseases, i.e. diseases, the development of which is determined by a mutation of one gene.

Genomic and chromosomal mutations

Genomic and chromosomal mutations are the causes of chromosomal diseases. Genomic mutations include aneuploidy and changes in the ploidy of structurally unchanged chromosomes. Detected by cytogenetic methods.

Aneuploidy- change (decrease - monosomy, increase - trisomy) of the number of chromosomes in the diploid set, not multiple of the haploid one (2n + 1, 2n - 1, etc.).

Polyploidy- an increase in the number of sets of chromosomes, a multiple of the haploid one (3n, 4n, 5n, etc.).

In humans, polyploidy, as well as most aneuploidies, are lethal mutations.

The most common genomic mutations include:

trisomy- the presence of three homologous chromosomes in the karyotype (for example, for the 21st pair, with Down syndrome, for the 18th pair for Edwards syndrome, for the 13th pair for Patau syndrome; for sex chromosomes: XXX, XXY, XYY);

monosomy- the presence of only one of the two homologous chromosomes. With monosomy for any of the autosomes, the normal development of the embryo is impossible. The only monosomy in humans that is compatible with life - monosomy on the X chromosome - leads (to Shereshevsky-Turner syndrome (45, X0).

The reason leading to aneuploidy is the non-disjunction of chromosomes during cell division during the formation of germ cells or the loss of chromosomes as a result of anaphase lagging, when one of the homologous chromosomes can lag behind all other non-homologous chromosomes during the movement to the pole. The term "nondisjunction" means the absence of separation of chromosomes or chromatids in meiosis or mitosis. The loss of chromosomes can lead to mosaicism, in which there is one e uploid(normal) cell line, and the other monosomic.

Chromosome nondisjunction is most commonly observed during meiosis. Chromosomes, which normally divide during meiosis, remain attached together and move to one pole of the cell in anaphase. Thus, two gametes arise, one of which has an extra chromosome, and the other does not have this chromosome. When a gamete with a normal set of chromosomes is fertilized by a gamete with an extra chromosome, trisomy occurs (that is, there are three homologous chromosomes in the cell), when a gamete without one chromosome is fertilized, a zygote with monosomy occurs. If a monosomal zygote is formed on any autosomal (non-sex) chromosome, then the development of the organism stops at the earliest stages of development.

Chromosomal mutations- These are structural changes in individual chromosomes, usually visible in a light microscope. A large number (from tens to several hundreds) of genes is involved in a chromosomal mutation, which leads to a change in the normal diploid set. Although chromosomal aberrations generally do not change the DNA sequence in specific genes, changing the copy number of genes in the genome leads to a genetic imbalance due to a lack or excess of genetic material. There are two large groups of chromosomal mutations: intrachromosomal and interchromosomal.

Intrachromosomal mutations are aberrations within one chromosome. These include:

—deletions(from lat. deletio - destruction) - the loss of one of the sections of the chromosome, internal or terminal. This can lead to a violation of embryogenesis and the formation of multiple developmental anomalies (for example, division in the region of the short arm of the 5th chromosome, designated as 5p-, leads to underdevelopment of the larynx, heart defects, mental retardation). This symptom complex is known as the "cat's cry" syndrome, since in sick children, due to an anomaly of the larynx, crying resembles a cat's meow;

—inversions(from lat. inversio - turning over). As a result of two points of breaks in the chromosome, the resulting fragment is inserted into its original place after turning by 180°. As a result, only the order of the genes is violated;

— duplications(from Lat duplicatio - doubling) - doubling (or multiplication) of any part of the chromosome (for example, trisomy along one of the short arms of the 9th chromosome causes multiple defects, including microcephaly, delayed physical, mental and intellectual development).

Schemes of the most frequent chromosomal aberrations:
Division: 1 - terminal; 2 - interstitial. Inversions: 1 - pericentric (with capture of the centromere); 2 - paracentric (within one chromosome arm)

Interchromosomal mutations, or rearrangement mutations- exchange of fragments between non-homologous chromosomes. Such mutations are called translocations (from Latin tgans - for, through + locus - place). This:

Reciprocal translocation, when two chromosomes exchange their fragments;

Non-reciprocal translocation, when a fragment of one chromosome is transported to another;

- "centric" fusion (Robertsonian translocation) - the connection of two acrocentric chromosomes in the region of their centromeres with the loss of short arms.

With a transverse rupture of chromatids through the centromeres, "sister" chromatids become "mirror" arms of two different chromosomes containing the same sets of genes. Such chromosomes are called isochromosomes. Both intrachromosomal (deletions, inversions, and duplications) and interchromosomal (translocations) aberrations and isochromosomes are associated with physical changes in the structure of chromosomes, including mechanical breaks.

Hereditary pathology as a result of hereditary variability

The presence of common species characteristics makes it possible to unite all people on earth into a single species of Homo sapiens. Nevertheless, we easily, with one glance, single out the face of a person we know in a crowd of strangers. The extraordinary diversity of people, both within a group (for example, diversity within an ethnic group) and between groups, is due to their genetic difference. It is now believed that all intraspecific variability is due to different genotypes that arise and are maintained by natural selection.

It is known that the human haploid genome contains 3.3x10 9 pairs of nucleotide residues, which theoretically allows to have up to 6-10 million genes. At the same time, the data of modern studies indicate that the human genome contains approximately 30-40 thousand genes. About a third of all genes have more than one allele, that is, they are polymorphic.

The concept of hereditary polymorphism was formulated by E. Ford in 1940 to explain the existence of two or more distinct forms in a population, when the frequency of the rarest of them cannot be explained only by mutational events. Since gene mutation is a rare event (1x10 6), the frequency of the mutant allele, which is more than 1%, can only be explained by its gradual accumulation in the population due to the selective advantages of the carriers of this mutation.

The multiplicity of splitting loci, the multiplicity of alleles in each of them, along with the phenomenon of recombination, creates an inexhaustible genetic diversity of man. Calculations show that in the entire history of mankind there has not been, is not and in the foreseeable future there will not be a genetic repetition on the globe, i.e. each person born is a unique phenomenon in the universe. The uniqueness of the genetic constitution largely determines the characteristics of the development of the disease in each individual person.

Humanity has evolved as groups of isolated populations living for a long time in the same environmental conditions, including climatic and geographical characteristics, diet, pathogens, cultural traditions, etc. This led to the fixation in the population of specific combinations of normal alleles for each of them, the most adequate to environmental conditions. In connection with the gradual expansion of the habitat, intensive migrations, resettlement of peoples, situations arise when combinations of specific normal genes that are useful under certain conditions in other conditions do not ensure the optimal functioning of some body systems. This leads to the fact that part of the hereditary variability, due to an unfavorable combination of non-pathological human genes, becomes the basis for the development of so-called diseases with a hereditary predisposition.

In addition, in humans, as a social being, natural selection proceeded over time in more and more specific forms, which also expanded hereditary diversity. What could be swept aside in animals was preserved, or, conversely, what animals saved was lost. Thus, the full satisfaction of the needs for vitamin C led in the process of evolution to the loss of the L-gulonodactone oxidase gene, which catalyzes the synthesis of ascorbic acid. In the process of evolution, humanity also acquired undesirable signs that are directly related to pathology. For example, in humans, in the process of evolution, genes appeared that determine sensitivity to diphtheria toxin or to the polio virus.

Thus, in humans, as in any other biological species, there is no sharp line between hereditary variability, leading to normal variations in traits, and hereditary variability, which causes the occurrence of hereditary diseases. Man, having become a biological species of Homo sapiens, as if paid for the "reasonableness" of his species by the accumulation of pathological mutations. This position underlies one of the main concepts of medical genetics about the evolutionary accumulation of pathological mutations in human populations.

The hereditary variability of human populations, both maintained and reduced by natural selection, forms the so-called genetic load.

Some pathological mutations can persist and spread in populations for a historically long time, causing the so-called segregation genetic load; other pathological mutations arise in each generation as a result of new changes in the hereditary structure, creating a mutation load.

The negative effect of the genetic load is manifested by increased mortality (death of gametes, zygotes, embryos and children), decreased fertility (reduced reproduction of offspring), reduced life expectancy, social disadaptation and disability, and also causes an increased need for medical care.

The English geneticist J. Hodden was the first to draw the attention of researchers to the existence of a genetic load, although the term itself was proposed by G. Meller back in the late 40s. The meaning of the concept of "genetic load" is associated with a high degree of genetic variability necessary for a biological species in order to be able to adapt to changing environmental conditions.

We used to say that each person is unique, implying a deep inner world, but sometimes people are born who are distinguished from the general mass not only by character, but also by appearance. We will talk about the 10 most terrible genetic mutations that occur in humans in isolated cases.

1. Ectrodactyly

One of the congenital malformations in which the fingers and / or feet are completely absent or underdeveloped. Caused by a malfunction of the seventh chromosome. Often the companion of the disease is the complete absence of hearing.

2. Hypertrichosis

During the Middle Ages, people with a similar gene defect were called werewolves or apes. This condition is characterized by excessive hair growth all over the body, including the face and ears. The first case of hypertrichosis was recorded in the 16th century.

3. Fibrodysplasia ossificans progressive (FOP)

A rare genetic disease in which the body begins to form new bones (ossificates) in the wrong places - inside the muscles, ligaments, tendons and other connective tissues. Any injury can lead to their formation: bruise, cut, fracture, intramuscular injection or operation. Because of this, it is impossible to remove ossificates: after surgery, the bone can only grow stronger. Physiologically, ossificates do not differ from ordinary bones and can withstand significant loads, but they are not in the right place.

4. Progressive lipodystrophy

People suffering from this unusual ailment look much older than their age, which is why it is sometimes called "reverse Benjamin Button syndrome." Due to a hereditary genetic mutation, and sometimes as a result of the use of certain drugs in the body, autoimmune mechanisms are disrupted, which leads to a rapid loss of subcutaneous fat reserves. Most often, the adipose tissue of the face, neck, upper limbs and torso suffers, resulting in wrinkles and folds. So far, only 200 cases of progressive lipodystrophy have been confirmed, and it mainly develops in women. Doctors use insulin, facelifts, and collagen injections for treatment, but these are only temporary.

5. Yuner Tan syndrome

Yuner Tan syndrome (UTS) is characterized primarily by the fact that people suffering from it walk on all fours. It was discovered by Turkish biologist Yuner Tan after studying five members of the Ulas family in rural Turkey. Most often, people with SYT use primitive speech and have congenital brain failure. In 2006, a documentary film called "Family Walking on All Fours" was made about the Ulas family. Tan describes it this way: "The genetic nature of the syndrome suggests a reverse stage in human evolution, most likely caused by a genetic mutation, the reverse process of the transition from quadrupedalism (walking on four limbs) to bipedalism (walking on two limbs). In this case, the syndrome corresponds to the theory of intermittent balance.

6. Progeria

It occurs in one child out of 8,000,000. This disease is characterized by irreversible changes in the skin and internal organs caused by premature aging of the body. The average life expectancy of people with this disease is 13 years. Only one case is known when the patient reached the age of forty-five years. The case was recorded in Japan.

7. Epidermodysplasia verruciformis

One of the rarest gene failures. It makes its owners very sensitive to the widespread human papillomavirus (HPV). In such people, the infection causes the growth of numerous skin growths that resemble wood in density. The disease became widely known in 2007 after a video with 34-year-old Indonesian Dede Koswara appeared on the Internet. In 2008, the man underwent complex surgery to remove six kilograms of growths from his head, arms, legs and torso. New skin was transplanted onto the operated parts of the body. But, unfortunately, after a while the growths appeared again.

8. Proteus Syndrome

Proteus syndrome causes rapid and disproportionate growth of bones and skin caused by a mutation in the AKT1 gene. This gene is responsible for proper cell growth. Due to a malfunction in its work, some cells rapidly grow and divide rapidly, while others continue to grow at a normal pace. This results in an abnormal appearance. The disease does not appear immediately after birth, but only by six months of age.

9. Trimethylaminuria

It belongs to the rarest genetic diseases. There are no even statistical data on its distribution. In those suffering from this disease, trimethylamine accumulates in the body. This substance with a sharp unpleasant odor, reminiscent of the smell of rotten fish and eggs, is released along with sweat and creates an unpleasant fetid amber around the patient. Naturally, people with such a genetic failure avoid crowded places and are prone to depression.

10. Pigmentary xeroderma

This hereditary skin disease is manifested in the increased sensitivity of a person to ultraviolet rays. It arises due to the mutation of proteins responsible for repairing DNA damage that occurs when exposed to ultraviolet radiation. The first symptoms usually appear in early childhood (before 3 years): when the child is in the sun, he develops serious burns after only a few minutes of exposure to the sun. Also, the disease is characterized by the appearance of freckles, dry skin and uneven discoloration of the skin. According to statistics, people with xeroderma pigmentosa are more at risk of developing cancer than others - in the absence of proper preventive measures, about half of children suffering from xeroderma develop certain cancers by the age of ten. There are eight types of this disease of varying severity and symptoms. According to European and American doctors, the disease occurs in about four out of a million people.

We used to say that each person is unique, implying a deep inner world, but sometimes people are born who are distinguished from the general mass not only by character, but also by appearance.

We will talk about the 10 most terrible genetic mutations that occur in humans in isolated cases.

1. Ectrodactyly

2. Hypertrichosis

3. Fibrodysplasia ossificans progressive (FOP)

4. Progressive lipodystrophy

5. Yuner Tan syndrome

6. Progeria

7. Epidermodysplasia verruciformis

8. Proteus Syndrome

9. Trimethylaminuria

10. Pigmentary xeroderma

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Unfortunately, among us there are people who stand out from the crowd with something, at first glance, repulsive and terrible. These are genetic mutations that make a person different, not like everyone else. We can't help but talk about the most terrible mutations that humans can have ...

1. Ectrodactyly

A congenital malformation caused by a malfunction of the seventh chromosome. Manifested in the absence or underdevelopment of the fingers and / or feet. Often accompanied by total loss of hearing.

2. Hypertrichosis

This disease is characterized by excessive hair growth all over the body, including the face. The first case of hypertrichosis was recorded in the 16th century. In ancient times, such people were called werewolves or apes.

3. Fibrodysplasia ossificans progressive (FOP)

A rare disease in which the body forms new bones (ossificates) in the wrong places - inside the muscles, ligaments, tendons and other connective tissues. Trauma can provoke their formation - a bruise, a cut, a fracture, even an intramuscular injection or operation. It is impossible to remove ossificates - after removal, the bone can grow even more ...

4. Progressive lipodystrophy

"Reverse Benjamin Button Syndrome" - this is also called the disease, because people suffering from it look much older than their real age. Due to a hereditary genetic mutation or the use of certain drugs, autoimmune mechanisms are disrupted, which leads to a rapid loss of subcutaneous fat reserves and the appearance of wrinkles and folds. So far, only 200 cases of lipodystrophy have been recorded, predominantly in women. The disease is not cured, doctors do collagen injections and facelifts, but this gives only a temporary effect.

5. Yuner Tan syndrome

People suffering from this syndrome walk on all fours, use primitive speech and have congenital brain failure. The disease was discovered by Turkish biologist Yuner Tan after studying five members of the Ulas family in rural Turkey. In 2006, a documentary was made about them called "Family Walking on All Fours". “The genetic nature of the syndrome suggests a reverse step in human evolution, most likely caused by a genetic mutation, the reverse process of the transition from quadrupedalism (walking on four limbs) to bipedalism (walking on two). In this case, the syndrome corresponds to the theory of punctuated equilibrium, ”the biologist explains his discovery.

6. Progeria

These are irreversible changes in the skin and internal organs caused by premature aging of the body. The disease occurs in one child in 8 million, they live an average of 13 years. In Japan, there was a single case recorded when a man with progeria lived to be 45 years old.

7. Epidermodysplasia verruciformis

People with this genetic disorder are very susceptible to the widespread human papillomavirus (HPV). This causes the appearance of dense growths on the body, resembling wood. The disease became widely known in 2007, when a documentary about 34-year-old Indonesian Ded Koswar was released. In 2008, the man underwent surgery to transplant "clear" skin onto his head, arms, legs and torso. But, unfortunately, soon the growths began to appear again ...

8. Proteus Syndrome

The syndrome is caused by a mutation in the AKT1 gene and is manifested by rapid and disproportionate growth of bones and skin. The AKT1 gene is responsible for the proper growth of cells, and when a failure occurs, some cells rapidly grow and divide, while others continue to grow at a normal pace. So the person begins to look abnormal. The disease manifests itself only six months after the birth of the child.

9. Trimethylaminuria

One of the rarest genetic diseases. In a person with this deviation, trimethylamine accumulates in the body - a substance with a sharp unpleasant odor, reminiscent of the smell of rotten fish and eggs. It is released along with sweat and creates an unpleasant fetid cloud around the patient. Those suffering from trimethylaminuria are prone to depression and avoid crowded places.

10. Pigmentary xeroderma

Manifested by increased sensitivity of the skin to ultraviolet rays. The disease arises from the mutation of proteins responsible for repairing DNA damage that occurs when exposed to ultraviolet radiation. Freckles, dry skin, burns on the body, discoloration of the skin, the risk of cancer are common symptoms of xeroderma pigmentosa.