The FDA formally rejected Disc Medicine’s bitopertin for porphyria after questioning the link between the blood biomarker used in trials and clear clinical benefit. Disc, an early recipient of the agency’s new fast‑track voucher program, saw its shares tumble after the decision. The agency cited “uncertainties” in the biomarker‑to‑patient‑outcome bridge, underscoring lingering FDA skepticism of biomarker‑based approvals. Disc and regulators clashed over surrogate endpoints and evidentiary standards; the rejection highlights how new review pathways can still founder when clinical benefit is not directly demonstrated. The decision raises doubts about the practical value of the commissioner’s priority voucher program and signals that accelerated review status will not override conventional efficacy expectations. Investors and rare‑disease developers will watch follow‑on communications closely for how sponsors might redesign trials or submit additional outcome data.