Rare diseases: what are they, what types are there and 36 examples - medical - 2023



There are diseases that we all suffer at least once in our lives: gastroenteritis, flu, colds, rashes. Even sexually transmitted diseases or many types of cancer are unfortunately common in society.

All these diseases and disorders that have a high prevalence in society have a strong impact on public health, which is why research and the search for new effective diagnosis and treatment techniques is the order of the day.

Investing large amounts of money in the study of common diseases is "profitable", as many people will enjoy the new drugs, vaccines or detection techniques.

However, what happens when a disease is suffered by only a very small number of people? That research in it is not "profitable", since the studies are extremely expensive and only a very small percentage of the population will use the fruits of the research.

This is what happens with the so-called "rare diseases". In this article we will see what they are, we will analyze how many types there are and we will present examples of each of them.

What are rare diseases?

Although its definition varies depending on the country, the WHO considers that a disease should be classified as "rare" if it affects less than 5 out of 10,000 inhabitants. Therefore, they are disorders with a low incidence of 0.05%.

Although it is true that if we look at them one by one, the incidence of each disorder is very low, we must bear in mind that there are about 7,000 rare diseases. This means that, in total, 7% of the world's population is affected by some type of rare disease.

490 million people suffer from at least one rare disease. In Spain alone, there are approximately 3 million people affected by one of these 7,000 different disorders.

That they are so rare is because most of these diseases are due to genetic disorders. Human beings have between 30,000 genes, and each of them is made up of thousands of DNA molecules.

By simple biological chance, these molecules can be victims of mutations or unexpected changes, causing the gene in which they are found to not work properly.

This is what leads to a person suffering from a rare disease. Given the high number of genes in the human body and the fact that mutations can occur in any of them, it is explained both that there are many types of rare diseases and that their incidence is low.

Although most are due to these genetic disorders, there are also rare diseases due to infection by some rare pathogen.

  • Recommended article: "The 11 types of infectious diseases"

Having made it clear what a rare disease is, below we propose a way to classify them according to their type and present some examples of these disorders.

Rare diseases: the 12 types and examples

Genetic disorders can be located in any human gene. Some of these mutations can be so serious that they impede the development of the fetus, although some of them will allow the person to be born with some rare disease.

These rare diseases can affect any part of the body, both tissues and organs, with a severity that always depends on the type of disorder. Thus, they can be related to deformities, digestion difficulties, skin disorders, nervous system conditions, hormonal problems, etc.

Here we present the different types of rare diseases that we can observe in humans according to the part of our physiology that they affect.We will also present examples of rare diseases for each of the types.

1. Chromosomal deformities and abnormalities

Physiological deformities are caused by mutations in genes or by chromosomal disorders, that is, that they are damaged or that there is more (or less) than the account.

Humans have 23 pairs of chromosomes in our cells. Anything outside this value will be responsible for more or less serious conditions.

Genetic abnormalities are responsible for deformities and abnormalities that can cause disabilities that have a great impact on both the affected person and their family, since in many cases they cannot lead an independent life.

Some examples of rare diseases of this type are:

1.1. Hutchinson-Gilford Progeria

Hutchinson-Gilford progeria is a rare syndrome characterized by premature aging. Although intelligence is not affected, the patient begins to suffer from alopecia, joint stiffness, skin damage and loss of subcutaneous fat from an early age.

This leads to premature death, usually due to damage to the blood vessels in the brain.

1.2. X fragile syndrome

Fragile X syndrome is a rare disease caused by an inherited defect on the X chromosome. Despite being a rare disorder, it is still the most common inherited cause of mental retardation. Also, after Down syndrome, it is the most typical chromosomal abnormality.

It affects more men, with an incidence in 1 in 4,000, and causes autistic behavior and mental retardation of varying degrees, anxiety and emotional instability.

1.3. Prader Willi syndrome

Affecting 1 in 25,000 people, Prader Willi syndrome is a rare disease in which embryonic development is not performed properly. Its most common clinical manifestations are mental retardation, hypogenitalism (the sexual organs are not well developed), hypotonia (the muscles never mature) and obesity.

2. Diseases of the digestive system

The digestive system is the set of organs that performs the absorption and digestion of food. It includes the mouth, stomach, liver, intestines, etc. Being made up of so many organs makes it susceptible to alterations in the genes that make their function not correct.

Some of the rare diseases that affect the digestive system are:

2.1. Primary biliary cholangitis

Primary biliary cholangitis is a rare disease involving the liver. It causes the bile ducts (the ones that send bile to the stomach to aid digestion) to be slowly destroyed.

This causes bile to accumulate in the liver and damage it, thus causing health problems: fatigue, abdominal pain, bone pain, high cholesterol, weight loss, etc.

2.2. Imperfect dentinogenesis

Dentinogenesis imperfecta is a rare disease that affects the mouth. Due to a genetic alteration, there is an abnormal development of the teeth. This disorder is hereditary, that is, it is passed from parents to children.

2.3. Necrotizing enterocolitis

Necrotizing enterocolitis is a rare disease that can be serious in newborns. This disease causes an inflammation of the colon, which ends up damaging the tissue of the large intestine.

It causes the child to not be able to absorb nutrients well, in addition to increasing the risk of infection.

3. Diseases of the nervous system

A healthy nervous system allows us to carry out the motor functions essential to lead an independent life. It also regulates the unconscious actions of our body, such as breathing and heartbeat.

Any genetic disorder that compromises the integrity of this nervous system can have serious consequences for health or, at least, affect the day-to-day life of the patient.

Some examples of rare diseases that affect the nervous system are:

3.1. Moebius syndrome

Moebius syndrome is a rare disease in which two important cranial nerves are not well developed at birth. These two nerves are responsible for controlling blinking and eye movement.

It therefore has serious implications such as facial paralysis and loss of expression. This can be accompanied by slurred speech and drooling.

3.2. Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis, better known as ALS, is a rare neurodegenerative disease that causes the progressive loss of function of motor neurons.

It usually manifests itself from the age of 40-60, at which point muscle deterioration begins to the point of causing death as a result of respiratory failure.

3.3. Congenital insensitivity to pain

Congenital insensitivity to pain is a rare disorder in which the autonomic nervous system is affected, the one in charge of perceiving stimuli. As a consequence, the patient is not able to interpret pain correctly. He doesn't feel it.

They must be constantly supervised since they run the risk of suffering serious injuries (trauma, burns, dislocations, etc.) without realizing it, which means that their life expectancy is lower than the average.

3.4. Gilles de la Tourette syndrome

Gilles de la Tourette syndrome, also known as the “tic disease”, is a rare disorder that affects the nervous system and is characterized by constant, involuntary and repetitive movements. They can be specific words or noises (sniffing, coughing, grunting, etc).

4. Skin and connective tissue diseases

The skin, subcutaneous tissue and connective tissue are also susceptible to some disorders in their physiology, which have different implications on the health of those affected.

Some examples of rare diseases in this group are:

4.1. Bullous epidermolysis

Epidermolysis bullosa is an inherited disorder characterized by unusual fragility of the skin and mucosa. This causes the patient to develop blisters with exaggerated ease after light friction or even for no apparent reason.

4.2. Marfan syndrome

Marfan syndrome is a rare inherited disease that affects connective tissue, that is, the fibers that hold the body's organs together. Depending on where the disorder is located, it can affect the heart, skeleton, eyes, blood vessels, etc.

Although the disease is life-threatening if the heart or blood vessels are affected, the most common manifestation is that patients have disproportionately large limbs. In addition, they are usually tall and thin people.

4.3. Dermatitis herpetiformis

Dermatitis herpetiformis is a rare disease that affects the skin and is characterized by the formation of small blisters and hive-like swellings on various parts of the body.

5. Endocrine and metabolic diseases

The endocrine system is the set of organs responsible for producing hormones, molecules that regulate all the functions of our body and participate in metabolic pathways.

  • Related article: "The 65 main types of hormones (and their functions)"

Disorders in the production of these hormones have implication in the physiology of the whole organism. Some examples of these diseases are the following:

5.1. Addison's disease

Addison's disease is a rare disorder characterized by the fact that the adrenal glands do not produce enough hormones. Located above the kidneys, these glands are responsible for releasing cortisol and aldosterone, two basic hormones for the body.

Not having enough of these hormones has serious consequences for the body: fatigue, low blood sugar, muscle pain, depression, hair loss, etc. It can even be deadly.

5.2. Cystinuria

Cystinuria is a rare inherited disease that causes errors in metabolic pathways. Cystine, an amino acid, is free and binds with other molecules. This causes kidney stones to form in the kidney, ureter, and bladder.

5.3. AL amyloidosis

AL amyloidosis is a rare disease that affects the shape of proteins. These do not have the structure that they should have and begin to deposit extracellularly causing damage to the organs. It can end up causing heart failure.

6. Diseases of the genitourinary system

The genitourinary system includes the urinary organs and those of the reproductive system. They are also susceptible to various diseases due to genetic disorders.

Some examples of these diseases are the following:

6.1. Interstitial cystitis

Interstitial cystitis is a rare disease characterized by inflammation of the bladder. This causes severe pain and a constant need to urinate.

6.2. Nephronoptysis

Nephronoptysis is a rare inherited disease that manifests itself from childhood and affects the kidneys. It ends up causing kidney failure that involves a transplant or dialysis treatment.

  • Related article: "The 15 most common kidney diseases"

6.3. Mayer-Rokitansky-Küster-Hauser syndrome: 1 / 5,000

Mayer-Rokitansky-Küster-Hauser syndrome is a rare disease characterized by a malformation during embryonic development of the Müllerian ducts, which in women form the fallopian tubes, uterus, cervix and upper part of the vagina. This causes problems in the fertility of the woman.

7. Diseases of the immune system

The immune system is the set of cells endowed with the ability to detect and neutralize potential threats for our body.

Genetic errors in the development of this can cause it to be unable to fight infections and even to detect our body's own cells as pathogens that must be attacked.

Some of the rare diseases of this type are:

7.1. Common variable immunodeficiency

Common variable immunodeficiency is a rare disease characterized in that the cells of the immune system cannot make antibodies against pathogens, so that the body does not develop immunity to bacteria or viruses and the patient is always susceptible to re-infection by these .

7.2. Myasthenia gravis

Myasthenia gravis is a rare disease that affects the immune system, causing communication between nerves and muscles to break down. This implies a greater tendency for those affected to feel weak and fatigued, as well as difficulties in speaking, chewing and even having facial expressions.

7.3. Severe combined immunodeficiency

Severe combined immunodeficiency is a rare disease that occurs not because antibodies are not produced, but because the number of cells of the immune system (lymphocytes) is too low. This causes those affected to be extremely sensitive to all kinds of pathogen infections, since they cannot fight them.

8. Diseases of the respiratory system

That the respiratory system works properly is essential for the body, as it is responsible for obtaining oxygen for cells and eliminating carbon dioxide, a compound that is toxic to cells.

That is why genetic disorders that affect its functioning can lead to serious health problems. These are some of the rare diseases that affect the respiratory system:

8.1. Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a rare disease characterized by scarring of the epithelial tissue of the lungs, causing progressive dysfunction of lung function. This can end up causing severe respiratory failure.

8.2. Primary ciliary dyskinesia

Primary ciliary dyskinesia is a rare disease characterized by an affectation in both the upper (nose, throat and trachea) and lower (lungs) respiratory tracts, which ends up causing respiratory dysfunctions in the affected person.

8.3. Tracheal stenosis

Tracheal stenosis is a rare disease whose main clinical manifestation is a significant narrowing of the trachea. This has negative consequences for respiratory function, as not enough air reaches the lungs.

9. Eye diseases

The eyes are susceptible to different diseases. In another article we review which are the main infections that we can suffer in the eyes, although there are also genetic disorders that can affect their functionality.

  • Recommended article: "The 10 types of infections in the eye (causes and symptoms)"

Some of the rare eye diseases are:

9.1. Neurotrophic keratopathy

Neurotrophic keratopathy is a rare disease characterized by progressive degeneration of the cornea, initially leading to redness and loss of visual acuity. Over time it can lead to vision loss.

9.2. Retinopathy of prematurity

Retinopathy of prematurity is a rare disease that occurs in newborns. It causes blood vessels to grow within the retina, something that should not happen under normal conditions, as it is one of the few areas of the body where there should be no blood vessels. It can cause blindness in the affected person.

9.3. Duane retraction syndrome

Duane retraction syndrome is a rare disease that causes patients to have limited eye movement, which can lead to amblyopia, more commonly known as "lazy eye."

10. Diseases of the circulatory system

The circulatory system is made up of the set of tissues and organs that allow blood to reach all parts of the body. Its most important components are the heart and blood vessels.

  • Recommended article: "The 24 parts of the human heart (anatomy and functions)"

Given their importance, disorders that affect some of these structures can have serious health consequences. Some of the rare diseases of the circulatory system are as follows:

10.1. Pulmonary hypertension

Pulmonary hypertension is a rare disease characterized by unusually high blood pressure in the arteries of the lungs and heart. This hinders the proper flow of blood, which causes the heart muscle to progressively weaken. It can end up causing death from heart failure.

10.2. Henoch-Schöenlein purpura

Henoch-Schöenlein purpura is a rare disease that causes inflammation and rupture of blood vessels in the skin, intestines, kidneys, and joints. It usually causes skin rashes and, in specific cases, kidney damage.

10.3. Hypoplastic left heart syndrome

Hypoplastic left heart syndrome is a rare disease that is seen from the moment of birth and is characterized by poor development of the left part of the heart, which causes it to not be able to beat properly.

This ends up causing the heart not to pump the necessary amount of blood, which can have very serious health consequences.

11. Cancers

In another article we reviewed which were the most common types of cancer, and we saw that there are some with millions of new cases diagnosed each year.

  • Recommended article: "The 20 most common types of cancer: causes, symptoms and treatment"

But nevertheless, there are many other less common cancers that have a very low incidence in the population, which makes them considered rare diseases. Some of these cancers are:

11.1. Neuroblastoma

Neuroblastoma is a rare type of cancer that usually occurs in newborns or children. It develops from tissue of the nervous system and can appear in different parts of the body, although it usually does so in the adrenal glands, located above each of the kidneys.

11.2. Thyroid carcinoma

Thyroid carcinoma is a rare cancer that develops in the thyroid, a gland responsible for producing different types of hormones involved in many functions of the body.

  • Recommended article: "The 6 differences between hyperthyroidism and hypothyroidism"

The development of cancer in this gland causes the functions of regulating body temperature, weight, heart rate and blood pressure to be affected.

11.3. Dermatofibrosarcoma protruding

A protruding dermatofibrosarcoma is a rare type of cancer that develops on the skin and is characterized by the appearance of bumps near the surface of the skin. It does not usually spread beyond the skin, although it is advisable to apply an early treatment.

12. Infectious diseases

Throughout this list we have seen rare diseases that are produced by factors intrinsic to the person, that is, by their genetic endowment. But nevertheless, there are rare pathogens that can cause illness in people who were perfectly healthy before infection.

Most of these diseases are usually serious, and some examples of them are the following:

12.1. Kuru

Kuru is a serious neurodegenerative disease caused by a prion infection (a protein with infective capacity) that causes tremors, fever and cold. Its development is slow since it can be incubating for more than 30 years, although when symptoms appear, death after a year is almost inevitable

12.2. Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease is a rare disorder also caused by a prion that infects nerve tissues in the brain and spinal cord, causing dementia and eventually death. Better known as "mad cow disease."

12.3. Whipple's disease

Whipple's disease is a rare disorder caused this time by bacteria that infect the joints and digestive system. It ends up having life-threatening consequences for the affected person. Fortunately, it can be treated with antibiotics.

Bibliographic references

  • Eurordis (2005) "Rare Diseases: understanding this Public Health Priority". European Organization for Rare Diseases.
  • Orphanet Report Series (2019) “List of rare diseases and synonyms”. Rare Diseases Collection.
  • European Commission (2013) “Rare diseases: How Europe is meeting the challenges”. European Commission.