They’re called “rare diseases.” The term suggests they affect a handful of individuals, isolated cases, and medical exceptions. However, this impression is misleading. In France, more than 3 million people are affected by a rare disease. Worldwide, more than 300 million people live with one of the 7,000 rare diseases currently identified. This represents approximately 4% of the world’s population.
In reality, rare diseases are numerous, complex, and largely misunderstood. And while each of them affects a small number of patients—sometimes a few dozen, sometimes a few thousand—they combine to form a public health emergency that is often made invisible.
This article aims to address this paradox: how can we describe diseases that, together, affect millions of people as “rare”? And why is it time to change our collective perspective on these little-known but ubiquitous pathologies?
What are rare diseases?
In France and Europe, a disease is considered rare when it affects fewer than one in 2,000 people. This may seem like a small number. However, this definition encompasses an extremely diverse reality: genetic, metabolic, neurological, autoimmune, infectious, and even cancerous pathologies. Some affect only a few dozen people worldwide, others several thousand.
We also sometimes speak of orphan diseases, a similar but distinct term: it designates those for which there is no recognized treatment, even if they are not necessarily rare.
Among the best-known rare diseases are cystic fibrosis, sickle cell disease, and Sanfilippo syndrome, a pediatric neurodegenerative disease often compared to a form of Alzheimer’s in children.
A reality more common than we think
The term “rare disease” conjures up a sense of marginalization. But taken together, these pathologies affect a significant portion of the population. It is estimated that more than 3 million French people are currently living with a rare disease. In Europe, this represents approximately 30 million people, and more than 300 million worldwide, or nearly 4% of the global population.
In total, more than 7,000 rare diseases have been identified, and new ones are described every month. This impressive figure underscores the extent to which rare diseases are not so rare collectively, even if each, taken in isolation, affects few people.
The paradox is there: individual rarity creates an invisible mass. These diseases are often ignored by public policies, underfunded by research, and unknown to the general public. Yet, they represent a major public health issue.
Diagnostic Delay: an obstacle course
One of the first challenges faced by families affected by a rare disease is what is known as diagnostic delay. This refers to the delay—sometimes several years—between the onset of the first symptoms and the diagnosis.
This average delay is estimated at five years in France. It can be much longer when symptoms are atypical, fluctuating, or confused with other disorders. Some patients see several specialists, undergo numerous tests, and are even misdirected toward psychological disorders before the true cause is identified.
On top of that, this delay has serious consequences:
- Loss of therapeutic opportunity when a treatment exists,
- Psychological and financial exhaustion of families,
- Risk of guilt or tension within the family circle.
Access to a rapid diagnosis is, however, the first step toward care, acceptance, and, in some cases, the search for treatment.
The 4th National Rare Diseases Plan: an Increased Mobilization
Faced with these challenges, the Ministry of Health launched the 4th National Rare Disease Plan in February 2025, in partnership with the Ministry of Research. This plan covers the period 2025-2030 and aims to strengthen the detection, treatment, and research of rare diseases in France.
Key objectives include:
- Reduce diagnostic delays to less than a year in the majority of cases.
- Create or strengthen specialized reference centers for certain pathologies.
- Better coordinate medical data through a unified national registry.
- Accelerate clinical trials, particularly in the field of gene therapy.
- Facilitate access to care throughout the country, including in rural areas.
- Promote patient associations, considered essential partners.
The plan is part of a broader effort to make France a pioneer country in the fight against rare diseases, particularly by strengthening synergies between hospital medicine, basic research, and citizen initiatives. Digital innovation is also playing a growing role, with the development of diagnostic tools assisted by artificial intelligence and specialized telemedicine.
It is a whole ecosystem that needs to be mobilized: from adapting schools and workplaces to ensuring access to social support. For example, improving the training of teachers, employers, and public services on the specificities of rare diseases would help reduce misunderstandings and create a more supportive environment.
Moreover, this plan is welcomed with hope but also caution by patient associations. Its success will depend on its actual implementation on the ground, the mobilization of healthcare professionals, and the financial resources allocated to it. The challenge is significant: restoring visibility, support, and hope to the millions of people affected by these diseases, which are still too often relegated to the background.
