Rare Disease Day: Protecting the 300 Million Living with Rare Diseases

Today, on Rare Disease Day, the global health community unites to raise awareness for the over 300 million people worldwide living with a rare disease. This observance, first launched in 2008, has grown into a international movement with patient organizations from more than 60 countries and regions participating in awareness campaigns .

The scale of the challenge is staggering:

• Over 6,000 identified rare diseases – a number that continues to grow as medical science advances.
• 300 million affected individuals – equivalent to the population of a major continent.
• 70% of rare diseases begin in childhood.
• Approximately 95% of rare diseases lack FDA-approved treatments.

This article provides a comprehensive medical and pharmacovigilance perspective on rare diseases, exploring their definitions, the unique challenges of drug development, the phenomenon of drug-induced rare diseases, and the specialized safety monitoring required for orphan drugs.

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Section 1: What Are Rare Diseases? Definitions and Classifications

1.1 The Challenge of Defining “Rare”

Despite their global impact, there is no universally accepted definition of a rare disease. The concept of “rare” is relative and varies significantly by region, reflecting differences in population size, healthcare systems, and policy priorities .

1.2 Regional Definitions of Rare Diseases

Region/Country	Definition Threshold	Legislative Framework
United States	Affects < 200,000 Americans (prevalence < 0.75‰)	Orphan Drug Act (1983)
European Union	Prevalence < 0.5‰ (≤ 1 in 2,000)	EU Orphan Regulation (1999)
Japan	Affects < 50,000 patients (prevalence < 0.4‰)	Orphan Drug Regulation (1993)
Australia	Affects < 2,000 patients (prevalence < 0.11‰)	Orphan Drug Policy (1997)
South Korea	Affects < 20,000 patients (prevalence < 0.4‰)	Orphan Drug Regulation (2003)
Taiwan	Prevalence < 0.1‰	Rare Disease and Orphan Drug Act (2000)

Critical Insight: The absence of a globally harmonized definition creates challenges for international research collaboration, epidemiological tracking, and drug development. While the World Health Organization has been cited as defining rare diseases as affecting 0.65–1‰ of the population, this reference actually originates from a 1995 BMJ publication and does not represent an official WHO position .

1.3 The ICD Coding Gap

Currently, there is no special coding system for rare diseases within the International Classification of Diseases (ICD). This absence of a universally recognized coding system prevents reliable patient registration in national or international databases and hinders assessment of the economic and social effects of rare diseases .

Progress: The European Rare Disease Task Force has established a working group to collaborate with WHO on ICD revisions, aiming to provide the rare disease community with a uniform coding system .

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Section 2: The Orphan Drug Revolution

2.1 What Are Orphan Drugs?

Orphan drugs are medicinal products intended for the diagnosis, prevention, or treatment of rare diseases. Under normal market conditions, these drugs would not generate sufficient sales to justify development costs due to:

• High costs and risks of drug development.
• Insufficient knowledge of pathophysiological mechanisms.
• Difficulties conducting clinical trials with small patient populations.
• Limited potential market. 

2.2 Legislative Incentives Driving Innovation

The landmark US Orphan Drug Act of 1983 transformed the landscape by offering:

• Financial subsidies for research and development.
• Market exclusivity (7 years in the US, 10 years in the EU).
• Tax credits for clinical research costs.
• Fee waivers for regulatory applications.
• Fast track approval pathways.
• Protocol assistance from regulatory agencies. 

Similar legislation followed globally: Japan (1993), Australia (1997), EU (1999), Taiwan (2000), and South Korea (2003) .

2.3 Impact of Orphan Drug Legislation

Metric	Pre-Orphan Drug Act (Pre-1983)	Current Status
FDA-approved orphan drugs (US)	< 10 in preceding decade	Over 350 approved, helping ~12 million Americans
EMA orphan designations (EU)	Not applicable	720+ drugs designated; 63+ authorized
Annual orphan drug approvals	Negligible	US: average 15/year; EU: 10–12/year

2.4 Recent Orphan Drug Approvals: Case Examples

Skyclarys (Omaveloxolone) for Friedreich’s Ataxia

Approved by EMA in February 2024, Skyclarys is indicated for Friedreich’s ataxia in patients aged 16 years and older. This inherited disease causes progressive nervous system damage, coordination difficulties, cardiomyopathy, and increased diabetes risk. The approval was based on a study of 103 patients showing reduction in physical impairment measured by the modified Friedreich’s Ataxia Rating Scale (mFARS) .

Pharmacovigilance Note: Skyclarys is subject to additional monitoring due to limited pre-authorisation experience. Common side effects (affecting >1 in 10) include elevated liver enzymes, headache, weight decrease, nausea, vomiting, diarrhea, fatigue, and muscle spasms .

Deltyba (Delamanid) for Multidrug-Resistant Tuberculosis

Although tuberculosis is not typically considered a rare disease, multidrug-resistant strains affect limited populations, earning Deltyba orphan designation in 2008. It is used in combination therapy for pulmonary MDR-TB when standard regimens cannot be composed due to resistance or tolerability issues .

Conditional Approval: Deltyba received conditional marketing authorisation, requiring ongoing studies to confirm long-term effectiveness and safety .

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Section 3: Pharmacovigilance in Rare Diseases – A Specialized Challenge

3.1 The Limits of Traditional Pharmacovigilance Systems

Traditional post-approval pharmacovigilance systems perform optimally when patient numbers are high and safety data flow is regular. Rare disease therapeutics face unique surveillance challenges :

Challenge	Description	Pharmacovigilance Implication
Small patient populations	Some therapies have < 50 patients globally	Statistical thresholds fail; 1% of 10 reports = 0.1 events – creates false sense of safety
Geographic dispersion	Patients concentrated at specialized centers; scattered across continents	Multiple intermediaries in reporting chain → data loss or misinterpretation
Limited natural history data	Many diseases diagnosed in childhood with poor survival; new treatments extend survival into adulthood	Difficulty distinguishing disease progression from treatment effects
Multi-organ involvement	Rare diseases often affect multiple systems simultaneously	Unclear clinical picture; symptoms may reflect disease or drug
Regulatory complexity	Different agency expectations; multiple jurisdictions	Navigating conflicting requirements; maintaining PSURs every 6 months with minimal cases

3.2 The Problem of Underreporting in Rare Diseases

A survey of 18,000 individuals with rare diseases found that:

• 25% of patients waited 5–30 years before being correctly diagnosed.
• 40% were diagnosed incorrectly before receiving the correct diagnosis. 

These diagnostic delays mean that adverse event reporting may be attributed to the wrong condition, further complicating pharmacovigilance efforts.

3.3 The Evolving Regulatory Framework

In September 2025, FDA’s Center for Drug Evaluation and Research (CDER) and Center for Biologics Evaluation and Research (CBER) proposed the Rare Disease Evidence Principles (RDEP) process to facilitate drug approvals for very small populations (<1,000 patients in the US) with known genetic defects .

Key RDEP Features:

• Substantial evidence may be established through one adequate and well-controlled study (potentially single-arm).
• Confirmatory evidence may include:
  • Evidence of treatment effect on direct pathophysiology.
  • Relevant non-clinical model data.
  • Clinical pharmacodynamic data.
  • Case reports and expanded access data.
  • External controls or natural history studies. 

3.4 FDA Guidance for Rare Disease Drug Development

FDA has published multiple guidance documents addressing rare disease challenges, including:

• Natural history studies for drug development.
• Early drug development and pre-IND meetings.
• Slowly progressive, low-prevalence diseases with substrate deposition.
• Pediatric rare diseases using Gaucher disease as a model.
• Benefit-risk assessment frameworks. 

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Section 4: Drug-Induced Rare Diseases – A Pharmacovigilance Perspective

A critical but often overlooked aspect of rare diseases is that some may be caused by medications themselves. From a pharmacovigilance standpoint, detecting drug-induced rare diseases requires sophisticated signal detection methods and global data sharing.

4.1 Drug-Induced Insulin Autoimmune Syndrome (IAS)

A comprehensive 2025 study published in Diabetology & Metabolic Syndrome analyzed 228 FAERS cases and 263 published cases (1980–2024) to establish the first systematic epidemiological profile of drug-induced insulin autoimmune syndrome .

Key Findings:

Parameter	Result
Total agents identified	58 drugs with potential IAS associations
Novel pharmacovigilance signals	12 new associations (bevacizumab, sitagliptin, amlodipine, olmesartan)
Strongest signals	Thiol-containing drugs: captopril, methimazole, clopidogrel (PRR > 200)
Level 1 evidence (highest confidence)	Clopidogrel, captopril, omeprazole, methimazole
Demographics	Median age 66 years; male predominance (59.21%)
Geographic disparity	85.17% of literature cases from Asia

Clinical Implication: Clinicians should prioritize IAS in older patients with unexplained hypoglycemia exposed to antiplatelet agents or proton pump inhibitors. HLA-DRB1*04:06 genotyping may improve detection .

4.2 Drug-Induced Aplastic Anemia

Another 2025 study in the International Journal of Clinical Pharmacy analyzed FAERS data (2004–2024) to evaluate drug-induced aplastic anemia, a rare but life-threatening condition .

Key Findings:

Parameter	Result
Total cases identified	4,493 drug-related aplastic anemia cases
Significant drugs detected	593 drugs; 16 met stringent criteria
Most frequent	Temozolomide (n=148), methotrexate (n=126), busulfan (n=100), linezolid (n=90)
Other implicated drugs	Ribavirin, nivolumab, pembrolizumab, fludarabine, carboplatin, etoposide, cyclophosphamide
Risk factors	Male sex (OR=1.63); age >42 and weight >60 kg were protective
Time-to-onset	Median 299 days; most cases within 6 months

Pharmacovigilance Implication: This study provides a data-driven framework for early detection, but prospective studies are required to confirm causality and refine individual risk predictions .

4.3 Other Drug-Induced Rare Diseases

Rare Disease	Known Drug Associations	Pharmacovigilance Challenge
Drug-induced lupus erythematosus	Procainamide, hydralazine, minocycline, TNF inhibitors	Distinguishing from idiopathic lupus
Drug-induced pulmonary arterial hypertension	Fenfluramine derivatives, dasatinib, interferon	Late recognition; irreversible damage
Drug-induced long QT syndrome	Many antiarrhythmics, antipsychotics, antibiotics	Rare but potentially fatal; genetic predisposition
Drug-induced thrombotic microangiopathy	Quinine, tacrolimus, cyclosporine, gemcitabine	Mimicking TTP/HUS; requires prompt recognition

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Section 5: The Paradox of Orphan Drug Safety – When Treatment Risks Are Severe

A fundamental challenge in rare disease pharmacovigilance is that patients and clinicians may accept significant adverse effect profiles because the alternative—no treatment—is often progressive disability or death. This creates a unique risk-benefit calculus.

5.1 Case Study: Skyclarys Adverse Effects

For Friedreich’s ataxia patients, Skyclarys offers the first approved treatment option. However, its side effect profile includes:

• Elevated liver enzymes (alanine transaminase and aspartate aminotransferase).
• Headache, decreased weight.
• Nausea, vomiting, diarrhea.
• Fatigue, mouth and throat pain.
• Back pain, muscle spasms.
• Decreased appetite. 

Risk-Benefit Analysis: The EMA concluded that despite uncertainties (small study numbers, exclusion of severe cases), the benefits seen justified authorization given the significant unmet medical need.

5.2 Case Study: Deltyba Safety Monitoring

Deltyba’s safety profile requires:

• Contraindication in patients with low albumin levels.
• Avoidance with certain interacting medications.
• Monitoring for QT prolongation (cardiac effects).
• Educational materials for healthcare professionals. 

5.3 The Risk-Benefit Question in Rare Diseases

From a pharmacovigilance perspective, a critical ethical and clinical question emerges:

Should we accept severe or life-threatening adverse effects from treatments for rare diseases because the underlying disease itself is devastating?

This question has no simple answer. Consider:

Perspective	Argument
Patient/family view	Any treatment offering hope may be acceptable despite risks
Clinician view	Must balance beneficence and non-maleficence; informed consent critical
Regulator view	Benefit-risk assessment must favor approval for unmet needs; post-marketing surveillance essential
Pharmacovigilance view	Every adverse event must be meticulously documented to refine risk profiles; signal detection remains crucial even for small populations

Example: A chemotherapy agent for a rare pediatric cancer may carry a 10% risk of secondary malignancy. Without treatment, mortality is 100%. The risk-benefit ratio favors treatment—but mandates lifelong surveillance and reporting.

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Section 6: The Future of Rare Disease Pharmacovigilance

6.1 Emerging Approaches

Approach	Description	Potential Impact
Patient registries	Systematic collection of real-world data	Larger datasets for signal detection
Natural history studies	Understanding disease progression without intervention	Distinguishing disease from drug effects
AI and machine learning	Summarizing literature; comparing data sources	Augmenting human expertise
Patient engagement	Direct input from patients and advocacy groups	Practical knowledge; communication preferences
Standardized methodologies	Developing frameworks for rare disease signal detection	Reducing variability and bias

6.2 The Role of Patient Advocacy Organizations

Organizations like NORD (US) and EURORDIS (Europe) have made significant progress in disseminating knowledge. However, disease registry networks are urgently needed to facilitate collaboration and ensure patients are not delayed access to orphan drugs .

6.3 Call for Global Harmonization

Priorities for the next decade:

1. Universal rare disease definition and ICD coding system.
2. Harmonized regulatory requirements across jurisdictions.
3. Shared patient registries enabling global signal detection.
4. Standardized pharmacovigilance methodologies for small populations.
5. Expanded orphan drug legislation in countries lacking frameworks. 

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Section 7: Practical Guidance for Healthcare Professionals

7.1 Recognizing Drug-Induced Rare Diseases

Clinical Scenario	Consider Drug-Induced Rare Disease
Unexplained hypoglycemia in elderly on antiplatelets/PPIs	Insulin autoimmune syndrome
Pancytopenia in patient on antiepileptics, antibiotics, or antineoplastics	Aplastic anemia
Unexplained thrombosis with immune thrombocytopenia	Drug-induced thrombotic microangiopathy
New-onset lupus symptoms after starting medication	Drug-induced lupus

7.2 Reporting Suspected Adverse Reactions

Healthcare professionals play a critical role in pharmacovigilance by reporting suspected adverse reactions to national centers. Each report contributes to global understanding of drug safety and may help identify signals that protect future patients.

What to report:

• Any suspected adverse reaction to an orphan drug.
• Unexpected therapeutic responses (may indicate misdiagnosis).
• Lack of efficacy (critical for progressive diseases).
• Any event in a rare disease patient, even if causality unclear.

7.3 Communicating with Rare Disease Patients

Principle	Application
Honesty about uncertainty	Acknowledge limited data; explain monitoring plan
Shared decision-making	Discuss benefit-risk calculus; respect patient values
Long-term follow-up	Establish surveillance plan; coordinate with specialists
Reporting encouragement	Ask patients to report any new symptoms promptly

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Conclusion: Equity Through Vigilance

Rare Disease Day reminds us that equity means fair access to diagnosis, treatment, care, and opportunities. For the 300 million people living with rare diseases worldwide, this equity depends on:

1. Accurate diagnosis – ending the diagnostic odyssey.
2. Access to treatments – through continued orphan drug incentives.
3. Safe therapies – through robust pharmacovigilance adapted to small populations.
4. Long-term surveillance – distinguishing disease progression from treatment effects.
5. Global collaboration – sharing data, knowledge, and resources.

From a pharmacovigilance perspective, rare diseases represent both the greatest challenge and the greatest opportunity in modern drug safety. The same small populations that make traditional signal detection difficult also demand our closest attention—because for patients with rare diseases, every adverse event matters, every report counts, and every signal could save lives.

As we mark Rare Disease Day 2026, let us commit to building pharmacovigilance systems that are as rare and special as the patients they serve—systems that are flexible, intelligent, patient-centered, and globally connected.

Because no patient should be too rare to be safe.

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References

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