The FDA issued a rejection letter for Disc Medicine’s bitopertin, the company’s experimental therapy for porphyria, after questioning the link between the trial’s blood biomarker and meaningful clinical benefit. The decision came even though the drug had been routed through the agency’s new priority-review voucher program. STAT reported the letter publicly, and investors reacted immediately with a sharp share decline. BioCentury followed the story and framed the decision as part of a pattern: regulators are increasingly skeptical of approvals based solely on surrogate biomarkers and of the new accelerated pathways. The FDA’s move raises fresh questions about the value and reliability of the commissioner’s voucher program and whether biomarker-driven development strategies can still deliver expedited approvals without stronger clinical correlates. For companies pursuing rare-disease programs, the ruling signals the need for clearer, patient-centered endpoints or additional confirmatory evidence.