From Orphan Drug to Platform Drug

Every major therapeutic platform in precision medicine was first proven in a rare disease. The pattern is consistent enough to be a law: rare disease goes first.

Antisense oligonucleotides were proven in spinal muscular atrophy. CRISPR gene editing was first applied in humans for sickle cell disease and transfusion-dependent beta-thalassemia. AAV gene therapy was validated through hemophilia and SMA. mRNA therapeutics were validated at pandemic scale for COVID-19 and are now being redirected toward rare metabolic diseases where the same lipid nanoparticle delivery system can provide enzyme replacement through a fundamentally different mechanism than traditional infusions.

In each case, the rare disease application came first because the conditions were most favorable: the biology was tractable (single gene, known mechanism), the unmet need was most urgent (children dying without treatment), the regulatory path was most accommodating (orphan drug designation, accelerated approval, small trial populations accepted), and the families were most willing to accept uncertainty (the alternative was no treatment at all).

The platforms built for rare disease are now treating common disease. The rare disease families who enrolled in the first trials are the reason those platforms exist.

The ASO Platform

Adrian Krainer and Frank Bennett developed nusinersen for spinal muscular atrophy. The drug is an antisense oligonucleotide that modifies RNA splicing of the SMN2 gene, forcing it to produce functional protein. The FDA approved it in December 2016.

The chemistry, the intrathecal delivery route, the toxicology profile, the manufacturing process, and the regulatory pathway established through nusinersen became the foundation for ASO programs targeting other neurological conditions. Ionis Pharmaceuticals, which collaborated with Krainer on nusinersen, now has ASO programs in clinical development for Huntington's disease, ALS, Alzheimer's disease, and more than a dozen other conditions. The company's pipeline contains over 40 ASO candidates across neurology, cardiology, and other therapeutic areas.

The milasen program at Boston Children's Hospital used the same ASO chemistry to design an individualized therapy for Mila Makovec's specific CLN7 Batten disease mutation. Timothy Yu's team adapted the platform, not the molecule. The nucleotide sequence changed. The delivery method, the manufacturing framework, and the safety profile were inherited from the work that nusinersen established.

Each new ASO built on the safety and manufacturing data generated by the previous ones. The first ASO required building the regulatory and manufacturing infrastructure from scratch. The hundredth ASO requires changing the sequence.

The CRISPR Platform

Casgevy (exagamglogene autotemcel), developed by Vertex Pharmaceuticals and CRISPR Therapeutics, received FDA approval in December 2023 as the first CRISPR-based therapy approved anywhere in the world. It treats sickle cell disease and transfusion-dependent beta-thalassemia. The therapy edits a person's own stem cells ex vivo (outside the body), reactivating fetal hemoglobin production to compensate for the defective adult hemoglobin. The corrected cells are returned to the body. They produce functional hemoglobin. The sickling stops.

The safety data, the manufacturing process, the regulatory framework, and the clinical evidence generated through Casgevy are now being applied to CRISPR programs for conditions far more common than sickle cell disease. Verve Therapeutics is using in vivo CRISPR editing to target PCSK9 for cardiovascular disease, a condition affecting hundreds of millions of people. Intellia Therapeutics is developing CRISPR-based therapies for transthyretin amyloidosis and hereditary angioedema. Editas Medicine is pursuing CRISPR for ocular conditions.

The regulatory precedent set by Casgevy, the first approval of a gene-edited cell therapy, established the framework within which every subsequent CRISPR therapy will be evaluated. The rare disease application built the road. The common disease applications will drive on it.

The AAV Gene Therapy Platform

Zolgensma, the AAV9 gene therapy for SMA, demonstrated that a viral vector could deliver a gene across the blood-brain barrier after a single intravenous infusion. That demonstration expanded the design space for neurology gene therapy programs that would not have been considered feasible before Zolgensma's data existed.

Hemgenix (etranacogene dezaparvovec), approved for hemophilia B in 2022, used an AAV5 vector to deliver the Factor IX gene to the liver. Roctavian (valoctocogene roxaparvovec), approved for hemophilia A in 2023, used an AAV5 vector to deliver a truncated Factor VIII gene. Elevidys (delandistrogene moxeparvovec), approved for Duchenne muscular dystrophy in 2023, used an AAV-rh74 vector.

Each approval refined the understanding of AAV vector safety, immunogenicity, durability, and manufacturing. The manufacturing capacity for AAV vectors, initially built for rare disease programs producing hundreds of doses per year, is now scaling to support programs that may require thousands or tens of thousands of doses. The contract development and manufacturing organizations (CDMOs) that built their AAV capabilities for rare disease clients are now serving gene therapy programs for cardiovascular disease, neurodegeneration, and metabolic syndrome.

The mRNA Platform

The COVID-19 pandemic validated mRNA-lipid nanoparticle delivery at a scale no rare disease program could have achieved: billions of doses manufactured and administered in under two years. The platform demonstrated that synthetic mRNA could direct human cells to produce a target protein (in the vaccine's case, the SARS-CoV-2 spike protein) safely and at scale.

That same platform is now being redirected toward rare metabolic diseases. The principle is identical: deliver mRNA encoding a missing enzyme to the liver, where cells translate the mRNA into functional protein. For conditions like methylmalonic acidemia, propionic acidemia, and galactosemia, mRNA therapy could provide enzyme replacement without the immunogenicity risks of infusing a foreign protein and without the permanence (and theoretical risks) of gene therapy. The mRNA degrades. The protein it produces is temporary. Repeat dosing maintains enzyme levels.

Proof-of-concept studies for GALT mRNA (for galactosemia) have shown restoration of galactose metabolism in animal models. The half-life of the mRNA remains a challenge: current formulations persist for roughly 14 days, which would require frequent dosing. But the manufacturing infrastructure, the lipid nanoparticle delivery system, and the safety database established through billions of COVID vaccine doses provide a foundation that no rare disease program could have built alone.

The Investment Logic

The conventional view of rare disease drug development is that it serves a small market. A condition affecting 10,000 people generates a fraction of the revenue of a condition affecting 10 million. The orphan drug incentives (market exclusivity, tax credits, fee waivers) exist because the market alone would not support development.

That framing misses the platform economics. A company that develops an ASO for SMA does not serve only the SMA market. It builds an ASO platform that can be adapted to dozens of conditions. The manufacturing expertise, the regulatory relationships, the safety database, the clinical trial infrastructure, and the intellectual property all transfer. The rare disease program is the proof of concept. The platform is the product.

Ionis Pharmaceuticals' market capitalization reflects its ASO platform, not the revenue from nusinersen alone. Vertex's position in gene editing reflects Casgevy plus the pipeline of CRISPR programs it enables. Novartis acquired AveXis (and Zolgensma) for $8.7 billion, a price that reflected the AAV gene therapy platform, not just the SMA franchise.

The rare disease families who participated in the clinical trials that validated these platforms were generating data that made the platforms investable. The safety data from 30 children with SMA in an early nusinersen trial is now cited in regulatory submissions for ASO programs targeting diseases that affect millions. The efficacy data from the first Casgevy trial informs the development of CRISPR therapies for cardiovascular disease.

The Data Requirement

Platform drugs compound in value only if the data from each application is captured, structured, and available to inform the next application. The long-term safety of AAV vectors, established through rare disease gene therapy programs, is the evidence base that common-disease gene therapy programs rely on for regulatory approval. If that safety data is locked in sponsor-controlled databases, fragmented across institutions, or lost when sponsors exit the market, the platform's compounding value is interrupted.

The safety profile of intrathecal ASO delivery, established through years of nusinersen follow-up in people with SMA, is directly relevant to every intrathecal ASO program that follows. The durability of CRISPR-edited stem cells, established through Casgevy follow-up in people with sickle cell disease, is directly relevant to every ex vivo gene editing program in development.

The people who received the first doses of these platform drugs are generating the long-term safety data that determines whether the platforms can expand. Their follow-up data is the most valuable dataset in precision medicine. Maintaining it, structuring it, and making it available for the next application is not a clinical courtesy. It is the mechanism by which rare disease cures become common disease cures.

The rare disease community did not choose to be the proving ground for precision medicine. The biology and the economics made the choice for them. What they can choose is whether the data they generate stays available, persists across sponsor transitions, and compounds in value over time, or whether it fragments and disappears when the next company acquires the last one and the filing cabinets change hands.