Rare Diseases

Rare conditions, commonly referred to as rare diseases, are those with a low incidence (fewer than 5 cases per 10,000 people). For this reason, knowledge about their features is limited, and the diagnostic process is often long and complex.

According to the World Health Organization (WHO), there are currently more than 7,000 rare diseases, which are classified into seven major groups:

• Rare genetic diseases: The majority of rare conditions have a genetic origin (estimated to be around 70%). Some of the most well-known include Angelman syndrome, Noonan syndrome, Fragile X syndrome, and Gilles de la Tourette syndrome.
• Rare infectious diseases: These are caused by the transmission of an extremely uncommon virus or bacterium. Examples include infectious encephalitis, viral hemorrhagic fever, hepatitis D, and tropical spastic paraparesis.
• Rare cancers: These are tumors that affect fewer than 6 people per 100,000. According to the Spanish Association Against Cancer, they account for between 22% and 24% of annual cancer diagnoses. Olfactory neuroblastoma, Merkel cell carcinoma, and vulvar cancer fall into this category.
• Rare toxic exposures: These occur when exposure to a toxic agent is highly uncommon or difficult to encounter. Examples include manganese poisoning, foodborne botulism, and colchicine poisoning.
• Rare immune diseases: These develop when the immune system mistakenly attacks the body’s own healthy cells. Some of the most recognized are hemophagocytic syndrome, primary immunodeficiency, and Behcet’s disease.
• Rare idiopathic diseases: These arise spontaneously with unknown causes, although some of the mechanisms involved can be identified. Common examples include idiopathic pulmonary fibrosis, idiopathic juvenile arthritis, and idiopathic achalasia.
• Undetermined rare conditions: Neither their causes nor their development mechanisms are known. The most well-known example is indeterminate colitis.

Although each of these conditions affects only a small number of individuals, many people living with a rare disease experience a reduced quality of life, including difficulties with social integration and increased vulnerability. One of the goals of the scientific community is to provide better resources for patients and their caregivers, as well as to alleviate the burden on the healthcare system.

Symptoms

There are no symptoms common to all rare diseases, as each one manifests in its own unique way.

Causes

Although most rare diseases originate from a genetic alteration, each one has its own set of causes, which are sometimes unknown.

Risk Factors

The main risk factor for developing a rare disease is a family history or the presence of genetic abnormalities.

Complications

Each rare condition has its own specific complications. However, the surrounding circumstances may lead any of them to result in:

• Social isolation
• Mental health disorders (stress, anxiety, depression)
• Economic vulnerability
• Late diagnosis, once symptoms are already advanced

Prevention

In most cases, rare diseases cannot be prevented. Those of infectious or toxic origin could theoretically be avoided by eliminating contact with the triggering agent, but such agents are typically unknown or extremely rare.

Which doctor treats rare diseases?

Geneticists are involved in diagnosing and treating most rare diseases, working in collaboration with specialists in the medical fields relevant to the organs affected in each specific case.