The number of various diseases that can significantly limit human life and even lead to death is constantly growing. At the same time, it is worth understanding an important fact: some of the pathologies that disrupt the functions of the body are not acquired, but, as they say, are rooted in genetics. We are talking about the inheritance of autosomal traits that are passed down from generation to generation.
What is meant by an autosomal trait
Deepening into the essence of this term, it is important first of all to pay attention to such a property of any living creature as heredity. In most cases, children are similar to their parents, but there are actually always certain differences among members of the same family.
In other words, everyone has their own individual characteristics, but they are actually part of the genetic heritage. Thus, an autosomal trait is nothing but the inheritance of the genetic traits of the parents.
Disease transmission
In addition to specific individual characteristics, a person can inherit some diseases from his father and mother. This fact is due to the influence of mutations in genes thatlocalized in autosomes. At the same time, such signs can be divided into two key areas: dominant and recessive. Both have a significant impact on the structure of the heritage of a particular person.
Autosomal dominant
Each type of inheritance has its own characteristics. If we consider autosomal dominant, then it is worth noting that in this case, in order to get the disease in a hereditary way, it is enough to transmit the mutant allele of any of the parents. Such a sign of inheritance can equally occur in both men and women. In essence, autosomal dominant inheritance can be defined as the transmission of a trait that is controlled by the dominant allele of an autosomal gene. With this type of inheritance, one mutant allele localized in the autosome will be enough for the manifestation of the disease.
The good news is that most diseases that are transmitted in this way do not cause significant harm to he alth, nor do they have a significant detrimental effect on human reproductive functions. If we compare the level of influence on the percentage of diseases, then dominant traits more often cause any deviations than recessive ones. In the presence of such a mutation in one of the spouses with the full he alth of the second, the risk of transmitting the disease is 50%. For this reason, an autosomal dominant trait, manifested in the form of a mutation, can be passed down from generation to generation and, thus, have a family character. Unlikeautosomal recessive, these traits appear in heterozygotes that have one mutant and one normal allele on homologous chromosomes.
Diseases in autosomal dominant inheritance
With this type of transmission of hereditary traits, a heterozygous carrier of the mutation is sufficient for the manifestation of the disease in the next generation. An interesting fact is that a dominant autosomal trait implies the same frequency of disease in both girls and boys.
If a disease resulting from this type of heredity transmission is present in a child, while both parents are he althy, then this fact means the occurrence of a new mutation in the germ cells of the mother or father. It is important to understand that in one family, the impact of a dominant gene on the condition of children may differ. This means that the clinical picture and the severity of the diseases will not necessarily be the same.
Examples of diseases
The autosomal trait of the dominant type is clearly manifested through a disease such as Marfan's syndrome. Such a diagnosis means that the connective tissue is affected in the human body. Patients suffering from Marfan's syndrome tend to have thin, thin fingers, and the length of the limbs is disproportionate. These people often develop malformations of the aorta and heart valves.
Another hereditary disease, which is determined by the presence of autosomal dominant traits of inheritance, is brachydactyly, it is also short-fingered. This is a fairly rare symptomone of the parents. The manifestation of this disease is noticeable already in the first time after birth due to an unnatural change in the phalanges of the toes and hands.
Hereditary deafness is an autosomal trait that can also be defined as dominant.
Amyotrophic lateral sclerosis (ALS, or Charcot's disease) is also a consequence of an autosomal dominant trait of inheritance and belongs to the group of motor-neuronal diseases. This disease can be defined as a fatal, progressive, neurodegenerative disorder that was caused by the degeneration of cells in the central nervous system - the motor neurons. The main function of these cells is to maintain muscle tone and ensure motor coordination.
Autosomal recessive trait: features
This type of inheritance has several key characteristics:
- may not affect the condition of children even if there were many carriers of a hereditary disease in the pedigree, since recessive traits do not appear in every generation (horizontal inheritance, unlike dominant traits);
- recessive mutant gene (a) appears phenopically only when it is in the homozygous state (aa);
- hereditary disease manifests itself equally often in both females and men;
- the likelihood that a born child will be sick increases significantly in the case of consanguineous marriages;
- Phenoptically he althy parents of a child with an apparent disease canbe heterozygous carriers of the mutant gene.
It is worth noting that among all hereditary pathologies, recessive autosomal inheritance of traits is the most common. Diseases that can be identified as a consequence of this symptom include a large group of fermentopathies leading to metabolic disorders, diseases of the blood (including homeostasis), kidneys, immune system, etc.
Examples of Autosomal Recessive Diseases
- This group of signs includes Gierke's disease (glycogenosis). The manifestation of this genetic disorder is due to a deficiency of the enzyme glucose-6-photosphatase, which leads to a significant deterioration in the ability of the liver to reproduce glucose. Violation of such an important process inevitably leads to hypoglycemia.
- Maple syrup disease is also an autosomal trait that can be defined as recessive. This disease has another name - leucinosis. Such a diagnosis implies a metabolic disorder resulting from improper metabolism of branched chain amino acids. This disease can be attributed to organic acidemia.
- Tay-Sachs disease, which also goes by names like early infantile amaurotic idiocy and hexosaminidase deficiency. This disorder is genetically autosomal recessive and results in progressive deterioration of the child's physical and mental abilities.
- It is worth noting that, unlike a disease such as deafness, the autosomal sign of color blindness isrecessive, but at the same time it can be classified as "sex-linked". Violation of color perception can be either partial or complete. The most common is the distorted perception of red. It is worth noting that in some cases, the impaired perception of a particular color is compensated by a better distinction between shades of other colors.
Phenylketonuria is an autosomal recessive trait that implies an inherited metabolic disorder. Such a violation is caused by a lack of the enzyme phenylalanine
What should be understood as sex-linked diseases
Diseases of this group are due to the fact that men have one X chromosome, and women have two. Accordingly, a male representative, having inherited a pathological gene, is hemizygous, and a woman is heterozygous. Hereditary traits that are transmitted in an X-linked manner may occur with different probability in both sexes.
If we consider the dominant X-linked inheritance of the disease, it is worth noting that such cases are more common in women. This is due to the increased possibility of obtaining a pathological allele from one of the parents. As for men, they are able to inherit this type of gene only from their mother. At the same time, in the male line, the dominant autosomal trait linked to the X chromosome is transmitted to all daughters, while the disease does not manifest itself in sons,because they don't get the father's chromosome.
If you pay attention to the autosomal recessive X-linked trait of inheritance, you will notice that such diseases develop mainly in hemizygous men. In turn, females are virtually always heterozygous and therefore phenoptically he althy. X-linked hereditary traits include diseases such as Duchenne-Becker muscular dystrophy, hemophilia, Hunter syndrome and others.
As for the Y-linked inheritance, these signs are due to the presence of the Y-chromosome exclusively in men. The action of such a gene can only be passed from father to son for many generations.
Features of the mitochondrial method of inheritance
This type of inheritance is distinguished among others by the fact that the transmission of traits occurs through mitochondria located in the plasma of the egg. At the same time, the ring chromosome is located in each mitochondria, and there are approximately 25,000 of them in the egg. Gene mutations in mitochondria appear when progressive ophthalmoplegia, mitochondrial myopathies and Leberaf optic nerve atrophy are present in the body. Diseases that are the result of this factor can be transmitted from mother equally often to both daughters and sons.
In general, both autosomal unlinked traits and other types of hereditary mutations can have a significant impact on the physical condition of several generations and are the cause of many serious diseases.
