From parents, a child can acquire not only a certain eye color, growth or face shape, but also genetic diseases transmitted by inheritance. What are they like? How can they be detected? What classification of hereditary diseases exists?
Mechanisms of heredity
Before talking about diseases, it is worth understanding what genetic heredity is. All information about us is contained in a DNA molecule, which consists of an unimaginably long chain of amino acids. The alternation of these amino acids is unique.
Fragments of a DNA strand are called genes. Each gene contains integral information about one or several signs of the body, which is transmitted from parents to children, for example, skin color, hair, character traits, etc. If they are damaged or their work is disturbed, genetic diseases that are inherited arise.
DNA is organized in 46 chromosomes or 23 pairs, one of which is sexual. Chromosomes are responsible for the activity of genes, their copying, as well as restoration during damage. As a result of fertilization, in each pair, there is one chromosome from the father, and the other from the mother.
In this case, one of the genes will be dominant, and the other recessive or suppressed. Simplistically, if the father’s gene responsible for eye color turns out to be dominant, the child will inherit this trait from him, and not from the mother.
Genetic diseases
Inherited diseases arise when violations or mutations occur in the mechanism of storage and transmission of genetic information. An organism whose gene is damaged will pass it on to its descendants in the same way as healthy material.
In the case when the pathological gene is recessive, it may not appear in future generations, but they will be its carriers. The chance that a dominant gene does not appear exists when a healthy gene also appears to be dominant.
Currently, more than 6 thousand hereditary diseases are known. Many of them appear after 35 years, and some may never declare themselves to the owner. With extremely high frequency, diabetes mellitus, obesity, psoriasis, Alzheimer's disease, schizophrenia and other disorders are manifested.
Classification
Inherited genetic diseases have a huge number of varieties. To divide them into separate groups, the location of the violation, the causes, the clinical picture, the nature of heredity can be taken into account.
Diseases can be classified according to the type of inheritance and location of the defective gene. So, it is important that the gene is located in the sex or non-sex chromosome (autosome), and is it overwhelming or not. Allocate diseases:
- Autosomal dominant - brachidactyly, arachnodactyly, ectopy of the lens.
- Autosomal recessive - albinism, muscular dystonia, dystrophy.
- Limited by gender (observed only in women or men) - hemophilia A and B, color blindness, paralysis, phosphate diabetes.
Quantitative-qualitative classification of hereditary diseases distinguishes gene, chromosomal and mitochondrial species. The latter refers to DNA disorders in mitochondria outside the nucleus. The first two occur in the DNA, which is located in the nucleus of the cell, and have several subspecies:
View | Causes | Disease |
Gene |
Monogenic | Mutations or lack of a gene in nuclear DNA. | Marfan syndrome, adrenogenital syndrome in newborns, neurofibromatosis, hemophilia A, Duchenne myopathy. |
Polygenic | The predisposition and action of exogenous factors. | Psoriasis, schizophrenia, coronary disease, cirrhosis, bronchial asthma, diabetes mellitus. |
Chromosomal |
| Changing the structure of chromosomes. | Syndromes of Miller-Dicker, Williams, Langer-Gidion. |
| Change in the number of chromosomes. | Syndromes Down, Patau, Edwards, Klaifentera. |
Causes of occurrence
Our genes tend to not only accumulate information, but also change it, acquiring new qualities. This is a mutation. It occurs quite rarely, about 1 time per million cases, and is transmitted to descendants if it occurs in germ cells. For individual genes, the mutation frequency is 1: 108.
Mutations are a natural process and form the basis of the evolutionary variability of all living things. They can be useful and harmful. Some help us better adapt to the environment and lifestyle (for example, the opposed thumb), others lead to disease.
The appearance of pathologies in genes is accelerated by physical, chemical, and biological mutagenic factors. Some alkaloids, nitrates, nitrites, some food additives, pesticides, solvents and petroleum products possess this property.
Among the physical factors are ionizing and radioactive radiation, ultraviolet rays, excessively high and low temperatures. The biological causes are rubella, measles, antigens, etc.
Genetic predisposition
Parents influence us not only upbringing. It is known that some people are more likely to have some diseases than others because of heredity. A genetic predisposition to disease occurs when one of the relatives has a gene disorder.
The risk of a specific disease in a child depends on his gender, because some diseases are transmitted only along one line. It also depends on the race of the person and on the degree of relationship with the patient.
If a person with a mutation gives birth to a child, then the chance of inheriting the disease will be 50%. The gene may well not manifest itself in any way, being recessive, and in the case of marriage to a healthy person, its chances of passing to descendants will already be 25%. However, if the spouse also owns such a recessive gene, the chances of its manifestation in posterity will again increase to 50%.
How to identify the disease?
In time to detect a disease or a predisposition to it will help the genetic center. Usually this is in all major cities. Before taking the tests, a consultation with the doctor is carried out to find out what health problems are observed in relatives.
A genetic examination is carried out by taking blood for analysis. The sample is carefully examined in the laboratory for any abnormalities. Future parents usually attend such consultations after pregnancy. However, it is worth coming to the genetic center during its planning.
Hereditary diseases seriously affect the mental and physical health of the child, affect life expectancy. Most of them are difficult to treat, and their manifestation is only adjusted by medical means. Therefore, it is better to prepare for this before the conception of the baby.
Down Syndrome
One of the most common genetic diseases is Down syndrome. It occurs in 13 cases out of 10,000. This is an anomaly in which a person has not 46, but 47 chromosomes. You can diagnose the syndrome immediately at birth.
Among the main symptoms are a flattened face, elevated corners of the eyes, a short neck and a lack of muscle tone. Auricles, as a rule, small, incision of the eyes oblique, irregular shape of the skull.
In sick children, concomitant disorders and diseases are observed - pneumonia, acute respiratory viral infections, etc. Exacerbations, for example, loss of hearing, vision, hypothyroidism, heart disease, may occur. Under Downism, mental development is slowed down and often remains at the level of seven years.
Constant work, special exercises and drugs greatly improve the situation. There are many cases when people with a similar syndrome could well lead an independent life, find work and achieve professional success.
Hemophilia
A rare hereditary disease affecting men. It occurs once in 10,000 cases. Hemophilia is not treated and arises as a result of a change in one gene in the sex X chromosome. Women are only carriers of the disease.
The main characteristic is the lack of protein, which is responsible for blood coagulation. In this case, even a minor injury causes bleeding, which is not easy to stop. Sometimes it manifests itself only the day after a bruise.
English Queen Victoria was a carrier of hemophilia. She transmitted the disease to many of her descendants, including Tsarevich Alexei - the son of Tsar Nicholas II. Thanks to her, the disease was called “royal” or “Victorian”.
Angelman's syndrome
The disease is often called "happy doll syndrome" or "Parsley syndrome", as patients experience frequent outbreaks of laughter and smile, and chaotic hand movements. With this anomaly, sleep disturbance and mental development are characteristic.
The syndrome occurs once per 10,000 cases due to the absence of some genes in the long arm of the 15th chromosome. Angelman's disease develops only if the genes are absent in the chromosome inherited from the mother. When the same genes are absent in the paternal chromosome, Prader-Willi syndrome occurs.
The disease cannot be completely cured, but symptom relief is possible. For this, physical procedures and massages are performed. Patients do not become completely independent, but during treatment they can serve themselves.