With the passage of time, sciences such as medicine have been progressively developed, something that has allowed life expectancy, quality of life and well-being to increase greatly.

As a result, many of the diseases that were once deadly can now be successfully treated, and in some cases the disease itself has even been eradicated. However, there are still different types of diseases that continue to pose a great challenge to medicine, such as AIDS, cancer or 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 which there is mostly no cure (although sometimes treatments can be found to reduce or slow down the symptoms, or correct, reduce or eliminate the affectation they cause in the subject and his daily life). We are talking about the set of hereditary diseases , a concept we will reflect upon throughout this article.

Hereditary diseases: what are they?

Hereditary diseases are the set of diseases and disorders that have 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.

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 that is given: it is possible that he or she is a carrier of a recessive gene that in him or her does not trigger the appearance of the disease, but this can develop in the descendants.

It is important to note that genetic diseases and hereditary diseases are not necessarily synonymous . Although all hereditary diseases are genetic, the truth is that the inverse relationship does not always have to be the case: there are genetic diseases that arise from de novo, spontaneous mutations that appear without any family history.

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

Types of gene transmission

To be able to talk about and know where hereditary diseases come from it is necessary to take into account the multiple methods of genetic transmission from which a mutated gene can be transmitted . In this sense, some of the main modes of genetic transmission are the following.

1. Autosomal dominant inheritance

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

In this case, there will be a 50% chance that each child that the person in question has will manifest the disease (depending on who inherits the dominant gene). It can be complete (one allele dominates over the other) or incomplete (two dominant genes are inherited, with 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 found in a recessive gene implies that the disease will not develop unless it exists on more than one allele of a chromosome, so that having a copy of that gene does not imply that the disorder has to appear .

For this to occur, both alleles of a gene must have the mutation, that is, both parents must pass on an altered copy of the gene to the child in order for the disease to develop.

3. Sex-linked inheritance

Although in order to be transmitted they have to be integrated into the sex cells, many of the hereditary diseases are autosomal, that is, the alteration is present in one of the non-sex chromosomes to be transmitted. However, other disorders are transmitted through copies of the sex, X or Y chromosomes . Since only males genetically carry Y chromosomes, if there is a disorder on this chromosome it can only be passed on from parents to their children.

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

4. Polygenic inheritance

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

5. Mitochondrial Inheritance

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

Examples of inherited diseases

There are many hereditary diseases, and thousands of them can be found. However, in order to put a face and a name to some hereditary diseases, we leave you with a total of a dozen examples (some of them very well known).

1. Huntington’s disease

Huntington’s disease, previously known as Huntington’s chorea , is an inherited disease with autosomal dominant transmission of complete penetrance.

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

2. Hemophilia

This dangerous disease, which is characterized by difficulty in clotting blood and causes profuse, uninterrupted bleeding that can be life-threatening if not stopped, is also a hereditary disease. Specifically its most common form, hemophilia A, is a sex chromosome-linked disease (specifically X-linked) and is transmitted in a recessive manner. 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 that it is difficult for them to appear.

3. Achondroplasia

Achondroplasia is a disorder of genetic origin that is characterized by 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 them we observe the presence of family history from which the mutation has been inherited. In these cases, an autosomal dominant pattern is observed, in which a single cup of the mutated gene may lead to the disease (if one parent has it, their children have a 50% chance of developing achondroplasia). The main associated genes are G1138A and G1138C.

4. Marfan’s disease

A disease of genetic origin that is characterized by the involvement of 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 at a cardiovascular level (particularly blows and affectations in the aorta that can be dangerous for life) or at an ocular level (there can be detachments of the retina, myopia and cataracts).

5. Cystic Fibrosis

Cystic fibrosis is one of the inherited diseases produced by an autosomal recessive inheritance, and is characterized by the accumulation of mucus in the lungs in such a way that it makes breathing difficult. Mucus can also appear in organs such as the pancreas, in which cysts can also appear . This is a disease that could be fatal, usually due to severe infections, which is more frequent in children and young people.

6. Leigh’s syndrome

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

Problems such as hypotonia, movement and gait problems, breathing problems, neuropathy and impaired heart, kidney and lung function are some of the common symptoms.

7. Sickle cell anemia

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

8. Thalassemia

Another blood-related disorder that is inherited through auosomal recessive inheritance is thalassemia. This disease causes the difficulty in synthesising specific parts of haemoglobin (especially alpha globin), something that can lead to the generation of a lower number of red blood cells and even generate anaemias of varying consideration and severity (although with treatment they can lead a normal life).

9. Duchenne muscular dystrophy

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

10. Phenylketonuria

Phenylketonuria is an inherited disease acquired through autosomal recessive inheritance, and is characterized by the absence or deficit of phenylalanine hydroxylase , which causes the inability to break down phenylalanine so that it accumulates in the body. This can lead to brain damage, and often results in delayed development, intellectual disability, uncontrolled movements and even seizures, as well as a peculiar smell of urine and sweat.

11. Leber Congenital Amaurosis

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

12. Autosomal dominant polycystic kidney disease

One of the most common hereditary kidney 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. Also frequent are the presence of kidney stones, pain, high blood pressure, strokes or cardiovascular problems (including mitral valve prolapse as one of the most frequent). It can even lead to end-stage renal failure. It is an autosomal dominant disease of complete penetrance, with mutations in the genes PKD1 and PKD2.

Bibliographic references:

  • Hib, J. & De Robertis, E. D. P. 1998. Fundamentals of cellular and molecular biology. Buenos Aires: El Ateneo.
  • Krakow, D. (2018). FGFR3 disorders: thanatophoric dysplasia, achondroplasia, and hypochondroplasia. In: Copel JA, D’Alton ME, Feltovich H, et al, eds. Obstetric Imaging: Fetal Diagnosis and Care.