FDA Official Clarifies Plausible Mechanism Framework Principles

The framework's concepts can be applied beyond just individualized therapies, says FDA's Teresa Buracchio.

Apr. 15, 2026 at 8:00am

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A glowing, vibrant neon outline of a human brain against a dark background, conceptually representing the FDA's efforts to approve therapies for rare diseases using a new regulatory framework.The FDA's plausible mechanism framework aims to provide a pathway for approving therapies that target the underlying causes of rare diseases, even when traditional clinical trials are not feasible.Arlington Today

The FDA's recently unveiled plausible mechanism framework was designed with individualized therapies in mind, but its principles can be applied to other therapies as well, according to Teresa Buracchio, M.D., head of the FDA's Office of Neuroscience. Buracchio explained that the framework is not a new approval pathway, but rather a set of regulatory principles being applied to reviewing customized therapies for the first time.

Why it matters

The FDA's plausible mechanism framework has caused confusion in the rare disease sector, with some companies like uniQure believing it should apply to their therapies even if they are not bespoke. Buracchio's comments aim to provide clarity on the framework's scope and how it can be used.

The details

Buracchio said the plausible mechanism framework 'shouldn't be a disadvantage' to non-individualized therapies, but it comes with a high regulatory bar that could make drug development in certain disease areas more challenging. The framework requires 'substantial evidence of effectiveness and a substantial improvement that's clear and distinct from the natural history of the disease,' which may be harder to demonstrate for slowly progressive diseases like Huntington's.

  • The FDA unveiled the plausible mechanism framework in 2026.
  • Buracchio's comments were made at the National Organization for Rare Disorders (NORD) symposium in Arlington, Virginia on April 15, 2026.

The players

Teresa Buracchio, M.D.

Head of the FDA's Office of Neuroscience and co-lead for writing the FDA's draft guidance on the new plausible mechanism framework.

Martin Makary, M.D.

FDA Commissioner who originally coined the term 'plausible mechanism pathway.'

Vinay Prasad, M.D.

Outgoing FDA director of the Center for Biologics Evaluation and Research (CBER).

David Margolin, M.D., Ph.D.

VP of clinical development at uniQure.

KJ

A patient who received a bespoke CRISPR base-editing therapy for carbamoyl phosphate synthetase 1 (CPS1) deficiency, which paved the way for the plausible mechanism framework.

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What they’re saying

“Plausible mechanism framework and individualized therapies are not interchangeable. We're talking about how you can use the principles of the plausible mechanism framework to support an approval of an individualized therapy. But you might be able to use the principles of the plausible mechanism framework to approve other therapies.”

— Teresa Buracchio, M.D., Head of the FDA's Office of Neuroscience

“Seeing a trend as early as one year in a 3,000, or 30,000, patient data set is a different matter than in the n of 10 in our control. I think it was just too early to see a mean change of sufficient magnitude at that point.”

— David Margolin, M.D., Ph.D., VP of clinical development at uniQure

What’s next

The FDA and uniQure, along with Huntington's disease organizations, are in active dialogue regarding how to interpret the data for uniQure's AMT-130 gene therapy.

The takeaway

The FDA's plausible mechanism framework is not limited to just individualized therapies, but its high regulatory bar could make drug development more challenging for certain slowly progressive diseases like Huntington's. The framework aims to balance the need for substantial evidence of effectiveness with the realities of small patient populations.