Optimizing Site Feasibility in Clinical Trials for Ultra-Rare Diseases

Why Site Feasibility is Especially Crucial for Ultra-Rare Trials

In ultra-rare disease clinical trials, where eligible patient populations may be limited to only a few individuals per country—or even globally—site feasibility takes on an elevated level of importance. A misstep in site selection can lead to zero enrollment, delays, protocol amendments, or even trial failure. Sponsors cannot afford traditional high-volume approaches or selection based on historical metrics alone.

Feasibility assessments in these studies must focus on disease-specific patient availability, diagnostic capacity, investigator expertise in rare pathologies, and local regulatory familiarity with orphan drug protocols. Effective feasibility processes enable targeted recruitment, reduced site burden, and streamlined regulatory navigation. Agencies like the EMA and FDA expect robust documentation showing rationale behind site selection for such sensitive research populations.

Challenges in Identifying Feasible Sites for Ultra-Rare Conditions

Key challenges in site feasibility include:

• Scattered patient populations: Patients may be spread across countries or continents
• Limited diagnostic infrastructure: Especially for genotypically defined subgroups
• Low investigator experience: Physicians may have managed only 1–2 cases ever
• Ethical and regulatory complexity: Local authorities may lack rare disease trial precedents

For example, in a lysosomal storage disorder trial targeting 12 global patients, one high-profile academic site failed to enroll due to lack of genetic testing facilities, despite clinical interest. Early feasibility vetting could have flagged this mismatch.

Steps in Conducting Rare Disease Feasibility Assessments

A structured feasibility process for ultra-rare studies involves:

1. Feasibility Questionnaire: Tailored to assess site’s access to target population, diagnostic tools, and previous rare disease experience
2. Patient Funnel Analysis: Estimating the number of patients diagnosable, consentable, and willing to participate within study timelines
3. Protocol Complexity Assessment: Determining alignment between study demands and site capabilities (e.g., need for sedation MRI, long-term follow-up)
4. Regulatory Landscape Review: Understanding IRB timelines, import/export rules, and pediatric approval pathways
5. Site Qualification Visits (SQVs): Virtual or on-site walkthroughs for infrastructure and PI engagement evaluation

These steps, executed sequentially, provide a risk-profiled site readiness score and inform go/no-go decisions with clarity.

Patient Mapping and Registry Utilization

Feasibility should include proactive engagement with national rare disease registries, patient advocacy groups, and reference centers. Mapping where patients are diagnosed, managed, and treated—not just where hospitals exist—is critical.

For instance, India’s Clinical Trial Registry and national disease registries can help sponsors assess where most of the genetically confirmed cases are clustered. Such data may suggest partnerships with local genetic labs or patient support NGOs to ensure effective outreach during recruitment.

Case Study: Multi-National Feasibility for a Pediatric Enzyme Replacement Trial

A sponsor planning a global trial for a pediatric metabolic disorder with 18 patients worldwide began by distributing a standard feasibility questionnaire. Despite 30 responses, only 8 sites could confirm access to more than 1 patient, and only 4 had proven ERT experience. Post-screening, 5 were qualified through remote SQVs. This focused approach led to 95% of planned enrollment in under 8 months.

Such precision feasibility ensured optimal site-to-patient ratio, regulatory readiness, and engagement from experienced clinicians—drastically reducing trial risk.

Feasibility in Decentralized or Hybrid Trial Models

Decentralized trial (DCT) elements are gaining traction in rare disease research. Feasibility must now include assessment of:

• Telemedicine infrastructure for follow-ups
• Home health visit availability for sample collection or infusions
• Local lab capabilities for urgent assessments
• eConsent and remote monitoring readiness

Ultra-rare disease trials may enroll just one or two patients per site—making hybrid or DCT components not just helpful but essential for trial execution.

Regulatory Expectations and Documentation

Agencies such as EMA, FDA, and PMDA expect site selection to be justified in the Clinical Trial Application (CTA) dossier. Key documents include:

• Site feasibility reports and questionnaires
• Rationale for geographic distribution of sites
• Documentation of site capabilities for protocol-specific procedures
• Backup site lists and criteria for substitution

During GCP inspections, regulators may question why non-performing sites were selected or why local approvals were delayed. A clear feasibility traceability matrix helps defend site selection rationale.

Conclusion: Precision Feasibility is a Cornerstone of Rare Disease Trial Success

In ultra-rare clinical trials, each patient is precious—and each site is strategic. A well-executed feasibility process minimizes trial risk, optimizes resource use, and accelerates timelines. Sponsors should invest in tailored feasibility assessments that go beyond numbers and focus on true site readiness for complex, high-stakes research.

From infrastructure and personnel to patient access and regulatory history, every data point matters. Precision in feasibility leads to precision in outcomes—both scientific and operational.