We are talking about incurable diseases that are passed from parents to children.
Hereditary diseases are those that, due to their genetic component, are likely to appear in offspring.
Some are caused by monogenic mutations, which facilitate the study of their transmissibility. Others are due to changes in networks of several related genes, which make it difficult to study their genetic causes and their degree of heritability.
Regardless of their type, these diseases cause health problems for many people that currently cannot be cured . In the future, these types of diseases may be prevented or controlled by gene therapy techniques, but today we can only treat the symptoms of these diseases.
The 10 most common hereditary diseases
Currently, more than 6,000 genetic diseases are known, which can be transmitted through generations. These diseases usually present variations in their frequency when we compare populations with different ethnic origins, due in part to the processes of genetic drift.
In some cases, these diseases offer protection against other more serious disorders that certain populations may suffer, such as sickle cell anemia.
1. Sickle Cell Anemia
Sickle cell anemia is an autosomal recessive genetic disease . This means that its genetic cause is found in autosomal chromosomes, that is, those that do not determine the sex of the individual (Neither the X chromosome nor the Y chromosome). Its recessive nature indicates that it is necessary to have two copies of the mutant gene for this disease to be expressed in the phenotype of the carrier individual.
Its prevalence is approximately 1 carrier per 150 people in Europe . This frequency varies enormously depending on the ancestral origin of each person, affecting 15-25% of the population of central and western Africa. As a result, African-Americans now have a 1 in 13 chance of carrying a sickle cell gene.
Sickle cell anemia causes the production of misshapen, sickle-shaped red blood cells due to a defect in the hemoglobin gene, the protein that is responsible for transporting oxygen. These misshapen erythrocytes have a much shorter average life, about 10 or 20 days compared to the usual 90 to 120 that a healthy red blood cell can last.
It is theorized that this disease is more frequent in populations exposed to malaria, since people with sickle cell anemia or carriers of a copy of these genes have a greater resistance to this disease, being a clear case of natural selection.
2. Cystic Fibrosis
Cystic fibrosis is the most common genetic disorder among Caucasian children. Its incidence is much lower in populations of Asian or African origin. In Europe, the number of carriers of mutations for cystic fibrosis is estimated at 1 in 10,000 people , but the exact number is unknown.
Cystic fibrosis is an autosomal recessive disease, where the CFTR gene on chromosome 7 is affected by a mutation. There are more than 1,250 characterized mutations of the CFTR gene, but 70% of cystic fibrosis cases are caused by the F508 mutation .
This disease is chronic and progressive, and can cause problems from birth. The CFTR gene mutation causes the production of thick, salty mucus, which causes blockages in various body systems. The most common problems they cause are at the level of the respiratory system (obstruction, recurrent infections) and sterility in men who have it.
- It might interest you: “Achondroplasia: what it is, causes, symptoms and possible treatments”
3. Down syndrome
Down syndrome is one of the best known genetic diseases. The individuals who present it have facial characteristics that make them easy to distinguish, in addition to causing a variable degree of intellectual disability and a tendency to present cardiac , endocrine or digestive system defects.
This inherited disease is extremely common, appearing in 1 in 1,000 births worldwide. There are factors such as the advanced age of the parents that increase the risk of having a child with Down syndrome.
It is caused by a chromosomal abnormality, a complete or partial third copy of chromosome 21. The risk of a person with Down syndrome passing their disease to their offspring is about 1/3.
4. Fragile X syndrome
Fragile X syndrome is dominantly associated with the X chromosome, one of the sex chromosomes. In this disease, the FMR1 gene on the X chromosome is transcriptionally silenced, caused by the presence of multiple extra three-nucleotide repeats (CGG) in the untranslated region of the gene.
This disease is more serious in men, since they only have one X chromosome . Females are less affected because they will have another working copy of the FMR1 gene on their second X chromosome.
Fragile X syndrome varies in its effects, depending on the severity of FMR1 silencing. It causes an intellectual deficit that includes problems with memory, language or behavior disorders similar to autism, in addition to presenting certain common physical features such as a narrow and elongated face, large ears and joint hypermobility.
5. Huntington’s disease
Huntington’s disease, also known as Huntington’s chorea, is a neurodegenerative disorder of the central nervous system. Those affected end up developing behavioral, psychiatric (such as dementia) and motor disorders, the so-called involuntary choreic movements.
This disease affects approximately 1 in 10,000 people in the Caucasian population. The average age of onset of symptoms is between 30 and 50 years, although it can also occur during adolescence. Once the first symptoms begin, the disease will not reverse.
It is an autosomal dominant hereditary disease, so those affected have a 50% chance of transmitting it to their direct offspring . It occurs due to the affectation of the huntingtin gene, on chromosome 4, due to the repetition of a nucleotide triplet (CAG). The more CAG triplets your patients present, the sooner they will begin to notice the symptoms of the disease.
6. Color blindness
Color blindness is the inability to see the normal color spectrum. It affects the cones, eye structures that allow us to discern colors. It is an X-linked recessive disease, so it will also affect males more frequently . It is estimated that 8% of men of Caucasian descent are color blind, while less than 0.5% of women have this disorder.
The cones make a distinction between the colors red, blue and green, with specialized cones for each of these colors. Depending on which ones are affected, the characteristics of color blindness will vary. The most common type is the one that causes difficulties in distinguishing red and green colors from each other.
7. Familial Hypercholesterolemia
Familial hypercholeserolaemia is a hereditary disease that affects approximately 1 in 250 people , although it is estimated that only 10% of those affected are diagnosed. This disease prevents the correct management of “bad cholesterol” (LDL), so that it accumulates easily in the circulatory system.
It can be treated with dietary control and other common strategies used to lower cholesterol levels, but in severe cases a procedure similar to dialysis must be used to lower blood LDL levels.
There are several mutations that can cause familial hypercholesterolemia, but the most common is the mutation of the LDLR gene , which codes for the low-density lipoprotein receptor. Some of these mutations are dominant, but others are recessive.
Those affected by familial hypercholesterolemia have a 50% chance of suffering from cardiovascular disease before the age of 55.
8. Thalassemia
Thalassemia is also a genetic disease related to hemoglobin dysfunction. There are two types, alpha and beta thalassemias, depending on the genes that have been affected . Together they are one of the most common monogenic hereditary disorders in the world, with a higher frequency in tropical and subtropical areas with the presence of malaria and also in the Mediterranean Sea area.
Hemoglobin has a modular structure, made up of two types of protein chains, the alpha and beta chains. The alpha chain is located on chromosome 16, while the beta chain is on chromosome 11. The type of thalassemia will depend on the type of chain that is affected.
Alpha thalassemia is autosomal recessive, while beta thalassemia can be either recessive or dominant depending on the mutation . There are several degrees of severity for these diseases, which depend on the genetic makeup of those affected.
9. Tay-Sachs disease
Tay-Sachs disease is autosomal recessive, occurring in 1 in 320,000 live births. Variants are described according to the age of onset of the disease, childhood, juvenile and adult, all of them caused by a dysfunction of the enzyme hexosaminidase A, which causes the accumulation of GM2 gangliosides, a lipid substance that accumulates in brain neurons.
Those affected by Tay-Sachs disease will experience paralysis, dementia, blindness, psychosis and deaths due to the degradation of the nervous system , which begins from the beginning of life. The infantile and juvenile variants cause the early death of those who suffer from it, usually not exceeding 15 years of life.
This disease is especially common in communities of Ashkenazi Jews , who tend not to establish conjugal relationships with people outside their community for religious reasons. 1 out of every 3,500 people in this group globally have this disease.
10. Duchenne muscular dystrophy
Duchenne muscular dystrophy is a disease that affects the neuromuscular level, through progressive muscle atrophy and weakness. It is an X-linked disease, so it mainly affects men, affecting 1 in 3,300 births .
Female carriers of this disease are usually asymptomatic, but they can also have a mild variant of the disease, called Duchenne and Becker muscular dystrophy. Children affected by this hereditary disease have delayed motor development, which prevents them from running and jumping in their first years of life. At 9.5 years old, on average, they lose the ability to walk.
Those affected by Duchenne muscular dystrophy usually die during adolescence due to cardiac or respiratory disorders related to the degeneration of smooth and cardiac muscles that this disease also causes.
Bibliographic references
- Data extracted from Orphanet (www.orpha.net/consor/cgi-bin/index.php?lng=ES) on 07/24/2019.
- WHO, Human Genomics in Global Health. Retrieved from www.who.int/genomics/public/geneticdiseases/en/index2.html on 07/24/2019.
- GeneticsAlliance. A Guide to Genetics and Health. Washington (DC): Genetic Alliance; 2006. Diseases that run in the family. Available at: www.ncbi.nlm.nih.gov/books/NBK115605/.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.
