The FDA rejected Disc Medicine’s bitopertin for a rare blood disorder, citing uncertainties about whether the trial biomarker correlates with clinical benefit, according to STAT. Bitopertin was the first experimental drug reviewed under the FDA commissioner’s new expedited-voucher program; the agency posted a complete response letter that sent Disc shares sharply lower. BioCentury’s reporting adds that the rejection follows a broader pattern of regulators pushing back on biomarker-only endpoints, intensifying debate over accelerated pathways and the value of new priority review vouchers. The decisions raise questions about the reliability of surrogate endpoints and the predictability of the agency’s expedited review programs for companies pursuing rare-disease approvals.