Rare Disease Clinical Trials 2026: Orphan Drugs, Basket Trials & How to Find Studies

Orphan Drug Designation: Incentives for Rare Disease Research

The Orphan Drug Act of 1983 was landmark legislation that transformed rare disease drug development. Before it, pharmaceutical companies had little financial incentive to develop treatments for diseases affecting fewer than 200,000 US patients — development costs were similar to common diseases, but the potential market was tiny. The Act created a package of incentives: 7-year market exclusivity (competitors cannot receive approval for the same indication), 50% tax credits on clinical trial costs, waived FDA application fees (saving ~$3 million), and faster FDA review.

The result has been dramatic: more FDA-approved treatments for rare diseases have been approved in the 40 years since the Orphan Drug Act than in all prior history of medicine combined. Over 600 orphan drugs have received FDA approval. In 2026, the FDA Office of Orphan Products Development (OOPD) grants approximately 400–500 orphan drug designations annually.

Rare Pediatric Disease (RPD) designation provides an additional incentive: a Priority Review Voucher (PRV) awarded upon approval — a transferable voucher that can be used or sold to another company for expedited FDA review of any drug. PRVs have sold for $100–350 million, creating a significant financial incentive specifically for childhood rare diseases. Companies including Ultragenyx, Sarepta, and bluebird bio have built business models partly around rare pediatric disease development and PRV monetization.

Adaptive Trial Designs for Small Populations

Traditional randomized controlled trials require hundreds or thousands of patients to achieve statistical power. For diseases affecting 500 or 5,000 patients globally, this is impossible. Innovative trial designs have been developed specifically for rare disease contexts:

Basket trials: Test a single drug (or drug class) across multiple different diseases or tumor types that share a common molecular feature — regardless of where in the body the disease manifests. The NCI-MATCH trial and KEYNOTE-158 are paradigmatic basket trials for cancer, testing pembrolizumab in any solid tumor with MSI-H/TMB-high status. For rare diseases, basket trials allow companies to test a drug across multiple ultra-rare conditions sharing a pathway (e.g., mTOR pathway diseases: TSC, PTEN hamartoma syndrome, Cowden syndrome).

Umbrella trials: Study multiple drugs within a single disease, using biomarker-based sub-stratification to match patients to therapies most likely to help them. The I-SPY2 breast cancer trial and LUNG-MAP are leading examples.

N-of-1 trials: Individualized crossover trials comparing multiple treatments within a single patient over time. Particularly relevant for ultra-rare diseases where assembling even 10 patients is impossible. The FDA's Complex Innovative Trial Design (CID) program explicitly facilitates N-of-1 and other adaptive designs.

External control arms: For diseases with very small patient pools, a placebo control arm may be replaced by a carefully matched historical control population from natural history registries — allowing all enrolled patients to receive the investigational drug. The FDA has increasingly accepted external controls with appropriate statistical methodology.

Natural History Studies and Patient Registries

Before a clinical trial can be designed, researchers need to understand the natural course of a disease: how it progresses, what the measurable outcomes are, what rate of change is expected without treatment, and what distinguishes mild from severe forms. Natural history studies — observational studies following patients over time without intervention — are foundational to rare disease drug development.

Patient registries are databases that systematically collect information about people with a specific disease over time. For many rare diseases, patient-driven registries established by advocacy organizations predate any pharmaceutical interest in the disease. The Cystic Fibrosis Foundation Registry, the Muscular Dystrophy Association registry, and thousands of disease-specific registries facilitate natural history research, identify trial-eligible patients, and connect researchers with patient communities.

Participating in a natural history study or registry is valuable even when no treatment trial is available — it contributes to the knowledge base that future trials will depend on, and registry participants are often the first to be notified when a trial opens. NORD (National Organization for Rare Disorders) maintains a comprehensive list of rare disease registries at rarediseases.org.

How to Find Rare Disease Clinical Trials

Finding trials for rare diseases requires a multi-pronged approach:

ClinicalTrials.gov: The most comprehensive database of registered trials. Search by disease name, synonym, or NCT number. Use the "Rare Disease" filter under "Condition." Set "Status" to "Recruiting" or "Not yet recruiting."

NORD's Clinical Trials Guide: rarediseases.org includes a patient-friendly trial finder and connections to disease-specific advocacy organizations with dedicated trial matching services.

NIH Undiagnosed Diseases Program (UDP): For patients without a diagnosis despite extensive workup. The UDP uses cutting-edge genomic and metabolomic testing to establish diagnoses and, when possible, connect patients with researchers studying relevant conditions.

Disease-specific foundations: For most rare diseases, patient advocacy organizations are the best-informed and most responsive sources for current trial information. They often have patient navigators who can help families evaluate trial options and logistics.

Expanded Access (Compassionate Use): If no trial is available, patients with serious conditions may qualify for expanded access to investigational drugs directly from manufacturers. The FDA's Expanded Access program allows physicians to request access to unapproved drugs for individual patients outside of a trial.

Key Takeaways

• The Orphan Drug Act's incentives (7-year exclusivity, tax credits, fee waivers) have driven hundreds of rare disease drug approvals since 1983.
• Basket trials, N-of-1 designs, and external control arms allow rigorous rare disease trials with patient populations too small for traditional RCT designs.
• Natural history registries are foundational — participating in one contributes to future trial design and gives early access to recruitment notifications.
• NORD (rarediseases.org), disease-specific advocacy organizations, and the NIH Undiagnosed Diseases Program are key resources for patients and families.
• Expanded Access allows physicians to request unapproved investigational drugs for individual patients outside of clinical trials when no approved treatment exists.