The 5 most common genetic diseases: causes, symptoms and treatment

The human being contains, in each of its cells, 23 pairs of chromosomes. Within each pair, one chromosome comes from the mother and another from the father, thus allowing for a characteristic known as diploidy. This trait is essential in the evolution of many species, since having two copies of the same gene (one maternal and one paternal), it is expected that one will be able to mask the faults that the other.

Thus, we can affirm that each gene that encodes our characteristics has two different variations or alleles, one on the relevant paternal chromosome and the other on the maternal one. It is said that an allele is dominant (A) when it is expressed regardless of its partner, while a recessive one (a) must have the other copy equal to it in order to manifest itself.

A person can be homozygous dominant for one gene (AA), homozygous recessive (aa), or heterozygous (Aa). In the latter case, the variant of the trait encoded by the dominant allele will always be expressed. With all this theory exposed and condensed, we are ready to tackle the 5 most common genetic diseases. Do not miss it, well

heritability is a fascinating mechanism that explains far more than meets the eye about medicine.

• We recommend you read: "Differences between syndrome, disorder and disease"

What are the most common genetic diseases?

Talking about genes without inheritance is an impossibility, because if a mutation in a specific gene causes a disease that does not cause infertility, we assume as a basis that the affected parent can transmit it to the offspring. Based on this premise, we show you some of the variants that are considered in heritability patterns:

• Monogenic diseases: its appearance is conditioned by the alteration of the sequence of a single gene. They can be autosomal (on non-sex chromosomes) or sexual, linked to the X and Y chromosomes. They can also be dominant (A) and recessive (a).
• Oligogenic diseases: several genes act in the manifestation of the clinical picture.
• Polygenic diseases: a combination of environmental factors and several genes encode the disease. Finding an exact causative agent in these cases is very difficult.

So that, a genetic disease does not have to respond to an exact mutation in a single gene. Multiple genome positions can encode dysfunctionality and, furthermore, in certain cases it is necessary for an environmental agent to trigger the underlying mechanisms. We go even further, since certain epigenetic markers (outside the genome) can induce the expression / inhibition of certain genes and modify the health of the individual.

As you can see, a genetic disease cannot always be categorized based on a mutated gene. Here are some examples of common genetic diseases in society, whether or not the exact mutations have been found. Do not miss it.

1. Polycystic kidney disease

Polycystic kidney disease suits us like a glove, as it is a known genetic pathology with Mendelian inheritance. We are facing a genetically heterogeneous condition with 3 genes involved: PKD1 (on chromosome 16p13.3), PKD 2 (on chromosome 4q21-23) or PKD3, although mutations in the former are much more common (85% of cases).

Respectively, These genes code for the polycystin 1 and 2 proteins, essential for the proper maintenance of the kidneys. The absence of functional polycystin encourages liquid cysts to appear in tissues, which increase in number and size over time and make the correct functionality of the devices impossible. kidneys.

Interestingly, this disease has two variants: autosomal dominant and autosomal recessive. The first is much more common than the second (remember that being dominant, one of the two alleles being mutated is enough) but, luckily, it is the less serious variant. On the other hand, recessive PKD is often fatal, as most infants who suffer from it die at birth.

Undoubtedly, polycystic kidney disease is the most common genetic disease in the world. It affects more than 12.5 million people throughout the Earth and its dominant variant is present in one in every 800 people, a not inconsiderable figure.

2. Down's Syndrome

Does this genetic disorder require presentation? More than a mutation in the genes, in this case we speak of a trisomy, since chromosome 21 occurs in the nucleus of cells with three distinct copies, instead of the two expected. 95% of patients with this syndrome owe the condition to an error during the second division meiotic, an essential process to give rise to the father's and mother's gametes before the fetus is fertilized.

Globally, the prevalence of Down syndrome is 10 per 10,000 live births, which implies about 8 million people with the condition. In any case, we prefer not to address these people as "patients" or "sick", but rather they are cases that translate into non-neurotypic patterns. The fact that something is outside the norm does not imply that it is always a pathological picture: changing the language is the first step to avoid systematic discrimination.

3. Cystic fibrosis

Cystic fibrosis is a genetic pathology of autosomal recessive inheritance, that is, the mutation that causes it is not found on the sex chromosomes and both copies of the mutant allele are required for it to occur.

In this case, we are dealing with mutations in the 7q31.2 gene, present on chromosome 7. This gene is responsible for encoding the cystic fibrosis regulatory factor, a mechanism that acts at the level of the membranes in affected tissues. Because it does not work properly, the patient generates an abnormally thick and sticky mucous substance that accumulates in the lungs and pancreas.

Its incidence varies between 1 in 3,000 and 1 in 8,000 live newborns, but it is very shocking to know that 1 in 25 humans are carriers of mutations in the 7q31.2 gene. Fortunately, since it takes two copies of such defective alleles for the disease to spread I developed, this does not manifest easily.

4. Thalassemia

Thalassemia is an inherited blood disorder that causes a decrease in the amount of hemoglobin in the organism of the patient. There are two clinical entities within this group, depending on whether the mutated genes are those that encode alpha globin (alpha thalassemia) or beta globin (beta thalassemia).

Be that as it may, 5% of the world population has mutated genes that are involved in the process of synthesis of hemoglobin and about 300,000 children are born with symptoms of thalassemia worldwide each year. Again, we are facing an autosomal recessive inherited disease, so both parents must have defective genes for their offspring to manifest it.

5. X fragile syndrome

It is the second genetic cause of intellectual disability worldwide, second only to Down syndrome. In short, this condition is caused by an abnormal increase in the number of nucleotides per repeat within the X chromosome, specifically in the FMR-1 gene. When the number of repeats exceeds a specific threshold, the gene loses its functionality.

This genetic event usually translates into a patient with mental deficiency, hyperactivity, repetitive speech, poor eye contact and low muscle tone, among many other clinical signs. It is associated with 1 in 4,000 men and 1 in 6,000 women, regardless of the ethnic group or social group analyzed. Although it is considered a rare disease, it is one of the most common within this group.

Resume

What did you think of this list? We have presented you with 5 of the most common genetic diseases, but of course there are many more. Without going further, up to 8,000 rare diseases are estimated in the world and 80% of them have an inheritable genetic basis. Practically, dysfunction can occur in as many genes as there are chromosomal organizations present in the body.

However, the undisputed queen of the list is polycystic kidney disease. By acting slowly and being autosomal dominant, it is relatively easy for a parent to pass the disease on to his offspring without realizing it. Recessive or lethal conditions at birth are much less common, for reasons reproductive factors you can imagine: if a person dies before leaving offspring, the mutation is not transmit.