When studying the nature of inheritance of various traits in humans, all known types of inheritance and all types of dominance are described. Many traits are inherited monogenic, i.e. are determined by one gene and are inherited in accordance with Mendel's laws. More than a thousand monogenic traits have been described. Among them there are both autosomal and sex-linked. Some of them are given below.
Monogenic diseases occur in 1-2% of the world's population. That's a lot. The frequency of sporadic monogenic diseases reflects the frequency of spontaneous mutation processes. Among them, a large proportion are diseases with a biochemical defect. A typical example is phenylketonuria.
Familial manifestation
Morphan's syndrome
This is a severe hereditary disease caused by a mutation in one gene that disrupts the normal cycle of phenylalanine conversion. In patients, this amino acid accumulates in cells. The disease is accompanied by severe neurological symptoms ( increased excitability), microcephaly (small head) and ultimately leads to idiocy. The diagnosis is made biochemically. Currently, maternity hospitals carry out 100% screening of newborns for phenylketonuria. The disease is curable if the child is promptly switched to a special diet that excludes phenylalanine.
Another example of a monogenic disease is Morphan's syndrome, or spider finger disease. A dominant mutation of one gene has a strong pleiotropic effect. In addition to increased growth of the limbs (fingers), patients experience asthenia, heart disease, dislocation of the lens of the eye and other anomalies. The disease occurs against the background increased intelligence, which is why it is called “the disease of great people.” It affected, in particular, American President A. Lincoln and the outstanding violinist N. Paganini.
Many hereditary diseases are associated with changes in the structure of chromosomes or their normal number, i.e. with chromosomal or genomic mutations. Thus, a severe hereditary disease in newborns, known as “ cry cat syndrome”, caused by the loss (deletion) of the long arm of chromosome 5. This mutation leads to pathological development larynx, which causes the baby's characteristic cry. The disease is incompatible with life.
Widely known Down's disease is the result of the presence in the karyotype of an extra chromosome from the 21st pair (trisomy of the 21st chromosome). The reason is the nondisjunction of sex chromosomes during the formation of germ cells in the mother. In most cases of extra chromosomes in newborns, the mother is at least 35 years old. Monitoring the incidence of this disease in areas with heavy pollution environment found a significant increase in the number of patients with this syndrome. It is also expected to influence viral infection on the mother's body during the maturation of the egg.
A separate category of hereditary diseases consists of syndromes associated with changes in the normal number of sex chromosomes. Like Down's disease, they occur when the process of chromosome segregation during gametogenesis in the mother is disrupted.
In humans, unlike Drosophila and other animals, the Y chromosome plays a large role in the determination and development of sex. If it is absent in a set with any number of X chromosomes, the individual will be phenotypically female, and its presence determines development towards the male sex. In particular, males with the chromosome set XXY + 44A are sick Klinefelter's syndrome. They are characterized mental retardation, disproportionate growth of the limbs, very small testes, lack of sperm, abnormal development of the mammary glands and other pathological signs. An increase in the number of X chromosomes in combination with one Y chromosome does not change the definition of male sex, but only enhances Klinefelter syndrome. The XXYY karyotype was first described in 1962 in a 15-year-old boy with significant mental retardation, eunuchoid body proportions, reduced testicles and hair growth. female type. Similar signs are characteristic of patients with the XXXYY karyotype.
Klinefelter syndrome (1) and Turner-Shereshevsky syndrome (2)
The absence of one of the two X chromosomes in a woman’s karyotype (XO) causes the development Turner-Shereshevsky syndrome. Affected women are usually short, less than 140 cm, stocky, with poorly developed mammary glands, and have characteristic wing-like folds on the neck. As a rule, they are infertile due to underdevelopment of the reproductive system. Most often, pregnancy with this syndrome leads to spontaneous abortion. Only about 2% of sick women remain pregnant until the end.
Trisomy (XXX) or polysomy on the X chromosome in women often causes a disease similar to Turner-Shereshevsky syndrome.
Hereditary diseases, associated with a change in the number of X chromosomes, are diagnosed by the cytological method by the number of Barr bodies or sex chromatin in the cells. In 1949, M. Barr and C. Bertram, studying the interphase nuclei of neurons in a cat, discovered an intensely colored body in them. It was present only in the cell nuclei of females. It turned out that it occurs in many animals and is always associated with gender. This structure is called sex chromatin, or Barr's bodies. Through careful cytological and cytogenetic analysis, it was found that sex chromatin is one of the two female sex chromosomes, which is in a state of strong spiralization and is therefore inactive. In women with Turner-Shereshevsky syndrome (XO karyotype), sex chromatin is not detected, as well as in normal men XY. Normal women XX and abnormal men each have one Barr body, and XXX women and XXXY men have two, etc.
Individuals with hereditary diseases are usually born with significant physical abnormalities, which allows the disease to be diagnosed early. But sometimes the disease does not make itself felt for months or even decades. For example, a severe hereditary disease caused by damage to the central nervous system — Huntington's chorea- can appear only after 40 years, and then its carrier has time to leave offspring. Patients are characterized by involuntary twitching movements of the head and limbs.
It happens that a person gives the impression of an absolutely healthy individual, but he has a hereditary predisposition to a certain disease, which manifests itself under the influence of external or internal factors. For example, some people have severe reactions to certain medications, which is caused by a genetic defect - the absence of a specific enzyme in the body. Sometimes there is a fatal reaction to anesthesia that seems completely healthy people, but in fact carrying a hidden special hereditary muscle disease. In such patients, during or after surgery under anesthesia, the temperature suddenly rises (up to 42°).
Hereditary diseases are those diseases that are transmitted through germ cells from generation to generation. In total, there are more than six thousand diseases of this type. About a thousand of them today can be identified even before the birth of a child. Also, these diseases can manifest themselves at the end of the second decade of life, and even after 40 years. The main reason The appearance of hereditary diseases are mutations of genes or chromosomes.
Classification of hereditary diseases
Hereditary diseases are divided into two groups:
- Single-cause or monofactorial. These are diseases that are associated with mutations in chromosomes or genes.
- Multicausal or multifactorial. These are diseases that appear as a result of changes in various genes and due to the influence of numerous environmental factors.
For the appearance of a similar disease in one of the family members, this person must have a similar or the same combination of genes that he already has. That is why hereditary diseases are associated with the presence of common genes among relatives of varying degrees of kinship.
And the proportion of common related genes
Since each first-degree relative of the patient has 50% of his genes, these people may therefore have an identical combination of genes that predisposes to the appearance of of this disease. Third- and second-degree relatives are slightly less likely to share the same set of genes with the patient.
Hereditary diseases - types
A hereditary disease can have more than one type. There are:
- Often when a cell divides, it happens that individual pairs of chromosomes remain together. As a result, the new cell has more chromosomes than others. This fact leads to these diseases occurring in 1 out of 180 newborns. These children have numerous birth defects development, etc.
- Disorders in autosomes lead to multiple and serious illnesses.
- Monogenic diseases involve mutations in one gene. These diseases are inherited according to Mendel's law.
- Hereditary metabolic diseases. Almost all gene pathologies are associated with hereditary metabolic diseases. When a mutation occurs during the construction of an operon, a protein with an incorrect structure is synthesized. As a result, pathological metabolic products accumulate, which is very harmful to the brain.
There are other hereditary diseases. Before starting their treatment, it is necessary to undergo a complete diagnosis. Doctors recommend that all expectant mothers who have patients with this diagnosis in their family be extremely careful. This is because such pregnant women must be under special supervision. Only in this case can the degree of manifestation of this disease in the baby be minimized. The main thing to remember is that any hereditary disease, with medical intervention at a certain desired period of time, can proceed much easier.
Not only can they be inherited external signs, but also diseases. Malfunctions in the genes of ancestors ultimately lead to consequences in the offspring. We will talk about the seven most common genetic diseases.
Hereditary properties are passed on to descendants from ancestors in the form of genes arranged in blocks called chromosomes. All cells of the body, with the exception of sex cells, have a double set of chromosomes, half of which comes from the mother, and the second part from the father. Diseases caused by certain malfunctions in genes are hereditary.
Myopia
Or myopia. A genetically determined disease, the essence of which is that the image is formed not on the retina, but in front of it. The most common cause of this phenomenon is considered to be increased length eyeball. As a rule, myopia develops during adolescence. At the same time, a person sees perfectly near, but poorly sees into the distance.
If both parents are nearsighted, then the risk of developing myopia in their children is over 50%. If both parents have normal vision, then the probability of developing myopia is no more than 10%.
Studying myopia, employees of the Australian National University in Canberra came to the conclusion that myopia is inherent in 30% of Caucasians and affects up to 80% of Asians, including residents of China, Japan, South Korea etc. Having collected data from more than 45 thousand people, scientists identified 24 genes associated with myopia, and also confirmed their connection with two previously established genes. All these genes are responsible for the development of the eye, its structure, and the transmission of signals in the eye tissue.
Down syndrome
The syndrome, named after English doctor John Down syndrome, which first described it in 1866, is a form of chromosomal mutation. Down syndrome affects all races.
The disease is a consequence of the fact that in cells there are not two, but three copies of the 21st chromosome. Geneticists call this trisomy. In most cases, the extra chromosome is passed on to the child from the mother. It is generally accepted that the risk of having a child with Down syndrome depends on the age of the mother. However, because young births in general are more common, 80% of all children with Down syndrome are born to women under the age of 30.
Unlike genetic disorders, chromosomal disorders are random failures. And there can be only one person in a family suffering from such a disease. But here, too, there are exceptions: in 3-5% of cases, rarer translocation forms of Down syndrome are observed, when the child has a more complex structure of the chromosome set. A similar variant of the disease can be repeated in several generations of the same family.
According to the Downside Up charity foundation, about 2,500 children with Down syndrome are born in Russia every year.
Klinefelter syndrome
Another chromosomal disorder. For about every 500 newborn boys, there is one with this pathology. Klinefelter syndrome usually appears after puberty. Men suffering from this syndrome are infertile. In addition, they are characterized by gynecomastia - an increase in mammary gland with hypertrophy of glands and adipose tissue.
The syndrome got its name in honor of the American doctor Harry Klinefelter, who first described clinical picture pathology in 1942. Together with endocrinologist Fuller Albright, he found out that if normally women have a pair of sex chromosomes XX, and men have XY, then with this syndrome in men there are from one to three additional X chromosomes.
Colorblindness
Or color blindness. It is hereditary, much less often acquired. Expressed in the inability to distinguish one or more colors.
Color blindness is associated with the X chromosome and is transmitted from a mother, the owner of a “broken” gene, to her son. Accordingly, up to 8% of men and no more than 0.4% of women suffer from color blindness. The fact is that in men, the “marriage” in the only X chromosome is not compensated for, since, unlike women, they do not have a second X chromosome.
Hemophilia
Another disease that sons inherit from their mothers. The history of the descendants is widely known Queen of England Victoria from the Windsor dynasty. Neither she herself nor her parents suffered from this serious disease associated with blood clotting disorders. Presumably, the gene mutation occurred spontaneously, due to the fact that Victoria’s father was already 52 years old at the time of her conception.
Victoria's children inherited the fatal gene. Her son Leopold died of hemophilia at age 30, and two of her five daughters, Alice and Beatrice, were carriers of the ill-fated gene. One of Victoria's most famous hemophiliac descendants is her granddaughter's son, Tsarevich Alexei, the latter's only son Russian Emperor Nicholas II.
Cystic fibrosis
A hereditary disease that manifests itself in disruption of the exocrine glands. It is characterized increased sweating, the secretion of mucus, which accumulates in the body and prevents the child from developing, and, most importantly, prevents the full functioning of the lungs. Likely death due to respiratory failure.
According to the Russian branch of the American chemical and pharmaceutical corporation Abbott, the average life expectancy of patients with cystic fibrosis is 40 years in European countries, 48 years in Canada and the USA, and 30 years in Russia. A well-known example is the French singer Gregory Lemarchal, who died at the age of 23. Presumably, Frederic Chopin also suffered from cystic fibrosis, and died as a result of lung failure at the age of 39.
A disease mentioned in ancient Egyptian papyri. Characteristic symptom Migraines are episodic or regular severe attacks of headache in one side of the head. The Roman physician of Greek origin, Galen, who lived in the 2nd century, called the disease hemicrania, which translates as “half a head.” The word “migraine” comes from this term. In the 90s In the 20th century, it was found that migraine is predominantly caused by genetic factors. A number of genes have been discovered that are responsible for the inheritance of migraine.
List genetic diseases*Main articles: hereditary diseases, Hereditary metabolic diseases, Enzymatic diseases. * In most cases, a code is also provided indicating the type of mutation and the chromosomes associated with it. See. also... ... Wikipedia
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A branch of human genetics devoted to the study of the role of hereditary factors in human pathology at all main levels of life organization from population to molecular genetic. Main section of M.g. is clinical genetics,... ... Medical encyclopedia
Hereditary diseases are diseases, the occurrence and development of which is associated with defects in the programming apparatus of cells, inherited through gametes. The term is used in relation to polyetiological diseases, in contrast to ... Wikipedia
Diseases, the occurrence and development of which are associated with defects in the programming apparatus of cells, inherited through gametes. The term is used in relation to polyetiological diseases, in contrast to the narrower group Genetic... ... Wikipedia
Hereditary disease is a disease, the occurrence and development of which is associated with defects in the programming apparatus of cells, inherited through gametes. The term is used in relation to polyetiological diseases, in contrast to ... ... Wikipedia
Hereditary metabolic disorders include large group hereditary diseases affecting metabolic disorders. Such disorders make up a significant part of the group of metabolic disorders (metabolic diseases).... ... Wikipedia
Books
- Childhood diseases, Belopolsky Yuri Arkadevich. The health of a child of any age is a special task for a doctor, because a growing organism requires more attention and greater vigilance in relation to diseases. Scheduled medical examinations, identification...
- Introduction to molecular diagnostics and gene therapy of hereditary diseases, V. N. Gorbunova, V. S. Baranov. The book outlines modern ideas about the structure of the human genome, methods for studying it, research on genes whose mutations lead to severe hereditary pathology: reviewed...
