Hereditary diseases: what are they, types, characteristics and examples?

This type of diseases can be transmitted in different ways, propagating mutations.

With the passing of time, sciences such as medicine have developed progressively, something that has allowed life expectancy, quality of life and well-being to increase to a great extent.

Thanks to this, many of the diseases that were once fatal can nowadays be successfully treated, and in some cases the disease itself has even been eradicated. However, there are still several types of diseases that continue to pose a great challenge to medicine, such as AIDS, cancer and diabetes.

In addition to these, there is a large group of diseases that have to do with the genes transmitted by our ancestors and for most of which there is no cure (although sometimes treatments can be found to reduce or slow down the symptoms, or to correct, reduce or eliminate the affectation they cause in the subject and his daily life). We are talking about the group of hereditary diseasesa concept on which we are going to reflect throughout this article.

Hereditary diseases: what are they?

They receive the name of hereditary diseases the set of diseases and disorders that present the diseases and disorders that present the particularity of being able to be transmitted to the descendants, that is to say from parents to children, through the transmission of the genes that cause them. that cause them.

Thus, these are diseases that arise at the chromosomal, mitochondrial or Mendelian level and are due to the existence of genetic mutations that come from our ancestors. It is not always necessary for one of the parents to manifest the disorder or disease, depending on the type of inheritance: it is possible that he or she is a carrier of a recessive gene that does not trigger the onset of the disease, but it may develop in the descendants.

It is important to keep in mind that genetic diseases and hereditary diseases are not necessarily synonymous.. Although every hereditary disease is genetic, the fact is that the inverse relationship does not always have to occur: there are genetic diseases that arise from de novo, spontaneous mutations, which appear without any family history.

For a disease to be inheritable, the genes and mutations linked to its appearance must be present in the germ cells, i.e. the sperm and/or eggs that will form part of the new being. Otherwise, we would be dealing with a genetic disease but not a hereditary one.

Types of gene transmission

In order to be able to talk about and know the origin of hereditary diseases, it is necessary to take into account the multiple methods of transmission of genes. it is necessary to take into account the multiple methods of genetic transmission by which a mutated gene can be transmitted.. In this sense, some of the main modes of genetic transmission are as follows.

Autosomal dominant inheritance

One of the main and best known types of inheritance is autosomal dominant inheritance, in which there is a mutation in one of the non-sex or autosomal chromosomes. The dominant gene will be the one that is always expressed, so that if there is a mutation in it linked to the appearance of a disease, it will be expressed and develop.

In this case, there will be a 50% chance that each child of the person in question will manifest the disease (depending on who inherits the dominant gene). It can have complete penetrance (one allele dominates the other) or incomplete penetrance (two dominant genes are inherited, the inherited traits being a mixture of those from the parents).

2. Autosomal recessive inheritance

Autosomal recessive inheritance is that which occurs when there is a mutation or alteration in a recessive gene and this is transmitted to the new generation. However, the fact that the alteration is in a recessive gene implies that the disease will not develop unless it exists in more than one allele of a chromosome, such that possessing a copy of such a gene does not imply that the disorder has to occur..

For the disorder to occur, both alleles of a gene must have the mutation, i.e. both father and mother must transmit an altered copy of the gene to the child for the disease to develop.

3. Sex-linked inheritance

Although they must be integrated into the sex cells in order to be transmitted, many inherited diseases are autosomal, i.e. the alteration is present in one of the non-sex chromosomes that will be transmitted. However, other disorders are transmitted through the copies of the sex chromosomes, X or Y.. Since only males at the genetic level carry Y chromosomes, if there is an alteration in this chromosome, it could only be transmitted from fathers to sons.

In the event that the alteration is on the X chromosome, it can be transmitted from both parents to the offspring regardless of their sex.

4. Polygenic inheritance

The two previous types of genetic inheritance are monogenic, i.e. they depend on a single gene. However, there are often multiple genes linked to a single gene, there are often multiple genes linked to the occurrence of a disease.. In this case we are talking about polygenic inheritance.

5. Mitochondrial inheritance

Although they are not as well known or common as the previous ones, there are several hereditary diseases and disorders that do not originate from the DNA present in the chromosomes, but rather from the organelles known as mitochondria.but their origin is to be found in the organelles known as mitochondria. DNA can also be found in these structures, although in this case it comes exclusively from the mother.

Examples of hereditary diseases

There are many hereditary diseases that exist, being possible to find thousands of them. However, in order to put a face and a name to some hereditary diseases, here are a total of a dozen examples (some of them very well known).

1. Huntington's disease

Huntington's disease, formerly known as Huntington's chorea, is a hereditary disease with transmission to the brain.Huntington's disease, is an inherited disease with autosomal dominant transmission and complete penetrance.

This disease is characterized by a progressive neurodegeneration that causes, among other symptoms, movement disorders (highlighting the choreic movement due to the involuntary contraction of muscles when moving), as well as a profound alteration of cognitive functions and especially of executive functions, which worsen with the passage of time.

2. Hemophilia

This dangerous disease, which is characterized by difficulty in Blood clotting and causes profuse and uninterrupted bleeding that can be life-threatening if not stopped, is also a hereditary disease. Specifically its most common form, hemophilia A, is a disease linked to the sex chromosomes (specifically linked to the sex chromosome). (specifically X-linked) and is transmitted recessively. This is why hemophilia is a disease that is suffered almost exclusively by males, since females possess two copies of the X chromosome in such a way as to make its occurrence more difficult.

3. Achondroplasia

Achondroplasia is a disorder of genetic origin that is characterized by causing characterized by causing alterations in the formation of cartilage and bone, being the main cause of dwarfism..

Although in most cases (about 80%) we are dealing with spontaneous mutations, in 20% of cases there is a family history of inherited mutations. In these cases an autosomal dominant pattern is observed, in which a single cup of the mutated gene can lead to the disease (if one of the parents has it, their children have a 50% chance of manifesting achondroplasia). The main associated genes are G1138A and G1138C.

4. Marfan disease

A disease of genetic origin that characterized by affecting the connective tissue. It is an autosomal dominant disease in which the bones grow in an uncontrolled manner, in addition to other possible symptoms such as cardiovascular (highlighting heart murmurs and aortic involvement that can become life-threatening) or ocular (there may be retinal detachment, myopia and cataracts).

5. Cystic fibrosis

Cystic fibrosis is one of the hereditary diseases caused by autosomal recessive inheritance, and is characterized by the accumulation of mucus in the lungs in such a way that it makes breathing difficult. The mucus may also appear in organs such as the pancreas, in which cysts may also appear.. It is a potentially life-threatening disease, usually due to severe infections, which is more common in children and young people.

6. Leigh Syndrome

In this case we are dealing with a hereditary disease of mitochondrial type (although it can also be caused by autosomal recessive genetic transmission), which is characterized by a rapid neurodegeneration that occurs early in life. characterized by rapid neurodegeneration that occurs early (usually before the first year of life) and in (usually before the first year of life) and in which the presence of damage to the brainstem and basal ganglia stands out.

Problems such as hypotonia, movement and gait problems, respiratory problems, neuropathy and impaired cardiac, renal and pulmonary function are some of the common symptoms.

7. Sickle cell anemia

This disorder is characterized by the presence of alterations in the shape of red blood cells. (instead of round, they become irregularly shaped and rigid) in such a way that they make possible the blockage of blood flow, as well as by a reduction in the life of these blood cells (something that can lead to a reduction in the levels of this essential component of blood). This is another hereditary disease, through autosomal recessive inheritance.

8. Thalassemia

Another blood-related disorder that is inherited through autosomal recessive inheritance is thalassemia. This disease causes difficulty in synthesizing specific parts of hemoglobin (especially alpha globin). (especially alpha globin), something that can cause a lower number of red blood cells to be generated and even generate anemias of varying severity and severity (although with treatment they can lead a normal life).

9. Duchenne muscular dystrophy

Characterized by progressive muscle weakness (both voluntary and involuntary muscle), the presence of frequent falls, constant fatigue and sometimes intellectual disability, this severe degenerative disease is primarily hereditary, with an X-linked recessive inheritance pattern.

10. Phenylketonuria

Phenylketonuria is a hereditary disease that is acquired through autosomal recessive inheritance, and is characterized by the absence or deficiency of phenylalanine hydroxylaseThis causes the inability to break down phenylalanine so that it accumulates in the body. It can lead to brain damage, and usually presents with maturational delay, intellectual disability, uncontrolled movements and even seizures, as well as peculiar odor of urine and sweat.

11. Leber's Congenital Amaurosis

A rare disease characterized by abnormalities or progressive degeneration of the photoreceptors of the retina. It can generate a great affectation at visual level, deteriorating the sense of sight and being usual that who suffers it has a very limited vision capacity. and being usual that the sufferer has a very limited vision capacity. It is an autosomal recessive inherited disorder.

12. Autosomal dominant polycystic kidney disease

One of the most frequent hereditary renal diseases, autosomal dominant polycystic kidney disease is characterized by the presence of cysts in both kidneys as well as secondarily in other organs such as the liver. Kidney stones, pain, arterial hypertension, strokes or cardiovascular problems (including mitral valve prolapse as one of the most frequent) are also frequent. It can even lead to end-stage renal failure. It is an autosomal dominant disease of complete penetrance, with mutations in the PKD1 and PKD2 genes.