Shares of Biohaven plunged 44.9% in the premarket on Wednesday after the company said the U.S. FDA issued a Complete Response Letter in response to its marketing application for its lead asset Vyglxia (troriluzole), rejecting the drug's approval.

The New Haven, Connecticut-based biotech had received the FDA’s priority review early this year for its new drug application (NDA) for troriluzole targeted at spinocerebellar ataxia, a group of rare neurodegenerative disorders.

In August, the regulator revoked a previously announced advisory committee meeting scheduled in connection with the NDA, raising the hopes for the drug’s potential approval.

However, the CRL has caught the company by surprise, with CEO Vlad Coric noting that "We are extremely disappointed on behalf of patients by this action from the Office of Neuroscience at FDA.”

The company said it will continue to engage the FDA as it looks to advance Vyglxia’s regulatory path further and expects to meet with the agency to discuss its next actions.

Concurrently, Biohaven (BHVN) announced a restructuring initiative to pause or delay its non-priority pipeline programs and achieve about a 60% reduction in annual R&D expenditure.