The Food and Drug Administration’s unexpected rejection of a gene therapy for the bleeding disorder hemophilia has reverberated through the biotech industry, potentially complicating the path to market for these one-time treatments.

In deciding not to approve Roctavian, a BioMarin Pharmaceutical gene therapy for hemophilia A, the FDA demanded two additional years of data to strengthen the case that its benefits are durable. That contrasts with the agency’s perceived leniency in approving previous one-time therapies for rare diseases, and it could affect the plans of other gene therapy companies hoping to win FDA approval based on early signs of promise….

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