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FDA Proposes ‘Plausible Mechanism’ Pathway for Individualized Rare-Disease Therapies

Sponsors would gain a route to approval based on plausible biology, with obligations to verify outcomes after launch.

Overview

  • The draft guidance outlines a route for genome-editing and RNA-based treatments to win approval for rare and ultra-rare conditions when randomized trials are not feasible.
  • Sponsors must justify trial infeasibility, show that the therapy targets the causal abnormality, leverage natural-history data, demonstrate on-target activity, and present evidence of clinical benefit.
  • Post-approval obligations include real-world evidence collection and confirmatory studies, with FDA warning it may withdraw products if commitments fail or results do not hold.
  • The agency kept manufacturing standards unchanged and encouraged master protocols and shared evidence across related products to speed development.
  • FDA opened a 60-day public comment period and expects a surge of applications, highlighting a CHOP/UPenn infant CPS1 case as a model and coming on the heels of moves to rethink the two-trial norm.