Rare disease trials demand years of investment to identify, genetically screen, enroll, and engage patients. When the study closes, that effort disperses. Community relationships may cool, and longitudinal data stops accumulating. The next program likely starts from scratch.
This pattern treats enrolled patients as a fixed cost of a single study. The alternative treats them as a compounding asset, a cohort that can anchor Phase 3, support a natural history study, inform an external control arm, and enable long-term follow-up in clinical trials across programs and years.
For sponsors running precision medicine, cell and gene therapy, and rare disease programs, the economics shift when patient relationships persist beyond the trial endpoint. A cohort recruited once can serve multiple regulatory and scientific needs. A patient consented once can contribute data across indications and timeframes. In this manner, the infrastructure that supported one study becomes the foundation for the next.
This article examines why the recruited cohort is so expensive to build, how regulatory obligations already require sponsors to maintain patient contact over years, and how to turn a one-time trial cohort into reusable infrastructure through patient registries and persistent engagement.
Rare disease trials operate under fundamentally different economics than common disease studies. The patient population is small, geographically dispersed, and often genetically heterogeneous. Finding patients who meet eligibility criteria is labor-intensive, and confirming a diagnosis or genetic variant requires screening. In turn, screening and extra steps can introduce attrition and friction.
Research from Tufts CSDD has shown that approximately 81% of screened patients in rare disease trials are ineligible and more than 56% of volunteers are not randomized. The funnel is narrow at every stage. The downstream consequences are well documented. Around 80% of clinical trials fail to meet their original enrollment timeline.
Rare disease trials magnify these existing trial challenges. Patient identification often requires outreach through specialty clinics, patient advocacy organizations, and genetic testing programs. Each enrolled patient represents months or years of upstream effort.
For sponsors working in rare disease patient recruitment, this creates a structural problem. The cohort is difficult and expensive to assemble, but the investment is written off when the trial closes. Patients who were pre-screened, genotyped, and engaged return to routine care. The relationship dissolves.
Each recruitment channel for a rare disease study requires coordination, and each enrolled patient represents a long sequence of touchpoints. The cost is cumulative, and the value is concentrated in a population that standard trial operations treat as temporary.
For gene therapy long-term follow-up (LTFU), regulatory expectations extend well beyond the primary endpoint. The FDA recommends fifteen years of long-term follow-up for gene therapy products that use integrating vectors, up to fifteen years for genome editing products, and up to five years for AAV vectors, each based on a product-specific risk assessment. Integrating vectors and genome editing technologies carry risks that may emerge over decades, while AAV vectors have a shorter recommended observation window.
The FDA also notes that the follow-up period will often not elapse before a product is licensed, so follow-up continues post-licensure, and the agency may recommend establishing patient registries to support ongoing data collection. This creates a practical challenge. Sponsors must maintain contact with patients across years, often across multiple sites and countries, using infrastructure designed for short-term trial execution.
Sano has written on the barriers to long-term follow-up in cell and gene therapy, including site turnover, patient relocation, and the operational complexity of sustaining engagement after trial sites close. Most sponsors lack a persistent engagement layer that continues independently of site infrastructure.
When LTFU is treated as a compliance burden, sponsors build the minimum viable system. They default to periodic outreach, manual tracking, and reactive contact attempts. When LTFU is treated as a strategic asset, the infrastructure looks different. It includes a patient registry that persists across trials, a direct-to-patient engagement channel, and a data layer that accumulates value over time.
FDA draft guidance on natural history studies states that natural history information "can play an important role at every stage of drug development, from drug discovery to the design of clinical studies... and beyond into the postmarketing period". In addition, natural history data can provide an external control group that lets sponsors collect longer-duration, larger-population data.
This creates a direct link between long-term patient engagement and regulatory strategy. A cohort that remains contactable after one trial can be re-enrolled into a natural history study. Data collected over years can inform trial design, support external control arms, and strengthen regulatory submissions.
Fewer than 5% of the more than 10,000 known rare diseases have an approved treatment, and rare diseases affect more than 30 million Americans. For many of these conditions, natural history data is sparse or nonexistent. Sponsors who initiate a natural history study early, and who maintain a persistent patient cohort, accumulate a dataset that supports multiple programs.
Paul Nioi, Senior Vice President of Translational Sciences at Alnylam, discussed this compounding logic on The Genetics Podcast. He described how a cohort originally studied for the HAO1 gene was later re-contacted to support a subsequent program. The original investment in patient identification and engagement carried forward into new research.
The compounding argument is structural. The same patients who supported a Phase 2 trial can contribute to a Phase 3, a natural history study, and a post-marketing registry. Each study adds data, and each touchpoint deepens the relationship. The value accumulates rather than resetting.
When established early, a patient registry allows sponsors to accumulate natural history data before a trial begins, identify eligible patients as protocols finalize, and maintain relationships with patients who screen out of one study but may qualify for another.
In a Sano-supported ultra-rare disease program, Sano maintained engagement with 84% of individuals who tested negative for the targeted gene variant, retaining them as a longitudinal data source and a re-contactable pool for future studies. These individuals were ineligible for the immediate trial but remained valuable for future programs.
This approach changes the economics of patient retention. Instead of losing 81% of screened patients to eligibility attrition, sponsors retain those patients in a registry where they can contribute data, receive updates on research progress, and be re-contacted when new trials open.
Sano has published patient engagement metrics across six rare disease studies, demonstrating that persistent engagement is operationally achievable. For a deeper look at recruitment challenges in this space, see Navigating rare disease patient recruitment.
The registry becomes the connective tissue between clinical trial enrollment, natural history studies, and long-term follow-up. It transforms a series of disconnected programs into a continuous relationship.
The argument for persistent patient engagement is economic and strategic. Sponsors already invest years and significant budget to build rare disease cohorts. Regulatory requirements for gene therapy long-term follow-up already demand sustained contact. Natural history studies already benefit from longer observation and larger populations.
The missing piece is infrastructure: a patient registry and engagement layer that persists across programs, captures longitudinal data, and enables re-contact. When that infrastructure exists, each trial builds on the last. The cohort compounds.
For sponsors in precision medicine, cell and gene therapy, and rare disease, the question is whether to treat each program as a fresh start or as an increment to a durable asset. The patients, the data, and the relationships can persist. The infrastructure to support that continuity is a choice.
To discuss how a persistent engagement approach could support your programs, get in touch.