What are the challenges associated with rare diseases?

There are fundamental challenges associated with rare diseases compared with common diseases, especially in terms of diagnosis.1 As outlined by the Global Commission to End the Diagnostic Odyssey for Children with a Rare Disease (https://www.globalrarediseasecommission.com/), patients with a rare disease may visit multiple physicians and specialists only to receive several misdiagnoses. Challenges to diagnosing rare diseases include: lack of information and awareness about rare diseases; minimal physician training on rare diseases; seemingly unrelated disease symptoms; limited access to diagnostic tools; lack of standardised criteria for diagnosis; shortage of geneticists; complex healthcare systems; and lack of communication among healthcare providers.2 The small patient numbers, problems in reaching patients who are widely dispersed across the world, a lack of validated biomarkers or surrogate endpoints, and limited clinical expertise and expert centres may also present significant barriers to diagnosing rare diseases.1 Moreover, the definition of a rare disease varies between countries (Figure 1).




The European Commission defines a rare disease as one that affects no more than 1 individual in 2000.3 In the European Union, rare diseases affect 6‒8% of the total population (around 27‒36 million people). Most rare diseases (80%) are of genetic origin; others may be degenerative or proliferative.4



The United States Orphan Drug Act defines a rare disease or orphan disease as a condition that affects fewer than 200,000 individuals in the United States. It is estimated that between 25‒30 million Americans live with a rare disease.5

Rare diseases in Japan, known as “rare and intractable diseases”, are defined as diseases with unknown aetiology with no effective treatment that present a major financial and psychological burden. Rare diseases in Japan are defined as affecting fewer than 50,000 patients in total in the country.6

In Australia, orphan drugs are indicated as treatments for the prevention or diagnosis of a life-threatening or seriously debilitating condition. The prevalence threshold for orphan drug eligibility criteria is treatment of a condition that affects fewer than 5 in 10,000 (or 1 in 2000) individuals.7

Figure 1.
What is the definition of a rare disease?


For many rare diseases, basic knowledge about the cause of the disease and its pathophysiology, natural course and epidemiology, is either limited or not available. This lack of information leads to difficulties in the diagnosis and treatment of rare diseases. As patients are located throughout the world, medical experts in these diseases may be scarce in specific geographical areas.1 However, researchers have made progress in learning how to diagnose and treat rare disorders, and the number of scientific publications regarding rare diseases is increasing.4,5

C-ANPROM/INT/FAB/0015; Date of preparation: March 2021