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

Over time, sciences like medicine have gradually developed, which has significantly increased life expectancy, quality and well-being.

Thanks to this, many diseases that were once fatal today can be successfully treated and in some cases have even managed to eradicate the disease itself. However, there are still different types of diseases that continue to pose a major challenge to medicine, such as AIDS, cancer or diabetes.

In addition to these, there is a large group of diseases linked to genes passed down from our ancestors and for which there is usually no cure (although sometimes treatments can be found to reduce or slow down symptoms, or correct, reduce or eliminate the effects they cause in the subject and in his daily life). We are talking about the set of hereditary diseases, A concept on which we will reflect throughout this article.

    Hereditary diseases: what are they?

    They are called hereditary diseases all of the diseases and disorders which have the particularity of being able to be transmitted to the offspring, that is to say from parents to children, by transmission of genes that cause them.

    Thus, these are diseases that occur 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 the disease, depending on the type of inheritance that is: it is possible that he is the carrier of a recessive gene that does not trigger in him the onset of the disease, but it can develop in the offspring.

    It is important to note that genetic diseases and inherited diseases are not necessarily synonymous. And while all inherited diseases are genetic, the truth is that the reverse relationship doesn’t always have to happen: there are genetic diseases that result from de novo, spontaneous mutations, that appear without a family history.

    For a disease to be hereditary, the genes and mutations linked to its appearance must be present in the germ cells, that is to say the spermatozoa and / or the ova which will be part of the new being. In another case, we would be dealing with a genetic disease but not hereditary.

    Types of gene transmission

    Being able to talk and know where hereditary diseases come from we must take into account the multiple methods of gene transmission from which a mutated gene can be transmitted. In this sense, some of the main modes of gene transmission are as follows.

    1. Autosomal dominant inheritance

    One of the main and most well-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 in the event of a mutation linked to the onset of a disease, it is expressed and developed.

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

    2. Autosomal recessive inheritance

    Autosomal recessive inheritance is that which occurs when there is a mutation or an alteration in a recessive gene and it is passed on to the next generation. However, the fact that the alteration is in a recessive gene implies that the disease will only develop if it is in more than one allele of a chromosome, so that having a copy of this gene does not mean that the disorder must appear.

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

    3. Inheritance linked to sex

    Although they must be integrated into the sex cells to transmit, many inherited diseases are autosomal, which means that the alteration is present in one of the non-sex chromosomes to be transmitted. However, other troubles they are transmitted by copies of the sex chromosomes, X or I. Since only men at the genetic level carry I chromosomes, if there is an alteration of this chromosome, it can only be passed from parents to male children.

    In the event that the alteration occurs on the X chromosome, they can be passed from both parents to children regardless of their gender.

    4. Polygenic inheritance

    Both types of genetic inheritance above are monogenic, that is, they depend on a single gene. however, there are often several genes linked to the onset of a disease. In this case, we are talking about a polygenic inheritance.

    5. Mitochondrial inheritance

    Although not as well known or common as the previous ones, there are several inherited diseases and disorders that do not originate from the DNA present on the chromosomesBut its origin is in organelles called mitochondria. In these structures we can also find DNA, although in this case it comes exclusively from the mother.

    Examples of hereditary diseases

    There are many hereditary diseases and it is possible to find thousands of them. However, in order to name and name some hereditary diseases, below we leave a total of a dozen examples (some of which are well known).

    1. Huntington’s disease

    Huntington’s disease, formerly known as Huntington’s disease, Is an inherited disease with autosomal dominant inheritance of complete penetrance.

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

      2. Hemophilia

      This dangerous disease, which is characterized by difficulties in blood clotting and causes heavy and uninterrupted bleeding that can be life threatening if left unchecked, is also an inherited disease. More precisely its most common form, hemophilia type A, is a disease linked to the sex chromosomes (Specifically linked to the X chromosome) and is inherited recessively. This is why hemophilia is a disease that almost exclusively men suffer from, because women have two copies of the X chromosome so that it is difficult for them to appear.

      3. Achondroplasia

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

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

        4. Marfan disease

        A genetic disease that is characterized by affecting connective tissue. It is an autosomal dominant disease in which the bones grow out of control, along with other possible symptoms such as cardiovascular disease (highlighting pockets and aortic damage that can be life threatening). ) Or at eye level (there may be retinal detachment, myopia and cataracts).

        5. Cystic fibrosis

        Cystic fibrosis is one of the inherited diseases caused by autosomal recessive inheritance and occurs characterized by the accumulation of mucus in the lungs in such a way that it makes it difficult to breathe. Mucus can also appear in organs like the pancreas, in which cysts can also appear. It is a disease that can be fatal, usually due to severe infections, which are more common in children and young people.

        6. Leigh syndrome

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

        Problems such as hypotonia, problems with movement and walking, breathing problems, neuropathy, and heart, kidney and lung failure are some of the common symptoms.

        7. Sickle cell anemia

        This disorder is characterized by the presence of changes in the shape of red blood cells (Instead of round, they take on an irregular shape and become rigid) in such a way that they help block blood flow, in addition to reducing the lifespan of these blood cells (which can lead to a reduction in blood flow). blood sugar). this essential component of blood). It is another inherited disease, by autosomal recessive inheritance.

        8. Thalassemia

        Thalassemia is another blood-related disorder inherited by recessive auosomal inheritance. This disease causes difficulty in synthesizing specific parts of hemoglobin (Especially alpha globin), which can reduce the production of red blood cells and even cause anemia of varying severity and severity (although with treatment they can lead normal lives).

        9. Duchenne muscular dystrophy

        Characterized by progressive muscle weakness (both in terms of voluntary and involuntary musculature), the presence of frequent falls, constant fatigue and sometimes intellectual disability, this severe degenerative disease is fundamentally hereditary, with a pattern of recessive inheritance linked to the X chromosome.

        10. Phenylacetonuria

        Phenylketonuria is an inherited disease that is acquired by autosomal recessive inheritance and is characterized by absence or deficiency of phenylalanine hydroxylase, Which causes the inability to break down phenylalanine in such a way that it builds up in the body. This can lead to brain damage and usually results in delayed maturation, intellectual disability, uncontrolled movements and even seizures, as well as a peculiar smell of urine and sweat.

        11. Leber’s congenital amaurosis

        Rare disease characterized by abnormalities or progressive degeneration of the retinal photoreceptors. This can lead to severe visual impairment, impairing the sense of sight and it is usual for the patient to have very limited vision. It is an autosomal inherited recessive disease.

        12. Autosomal dominant polycystic kidney disease

        One of the most common inherited kidney diseases, autosomal dominant polycystic kidney disease is characterized by the presence of cysts in both kidneys as well as secondary to other organs such as the liver. Kidney stones, pain, high blood pressure, spills, or cardiovascular problems (including mitral valve prolapse as one of the most common) are also common. It can even lead to end-stage kidney disease. It is a fully penetrating autosomal dominant disease, with mutations in the PKD1 and PKD2 genes.

        Bibliographical references:

        • Hib, J. & De Robertis, EDP 1998. Fundamentals of cell and molecular biology. Buenos Aires: the Athenaeum.
        • 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.

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