05:20 PM EDT, 09/23/2025 (MT Newswires) -- Biogen (BIIB) said late Tuesday that the US Food and Drug Administration has delayed approval of Spinraza, or nusinersen, for the potential treatment of spinal muscular atrophy.

The health regulator issued a complete response letter for the company's supplemental new drug application and asked for updated technical information related to its chemistry manufacturing and controls module, Biogen said.

The FDA did not cite any deficiencies in the clinical data of the high dose regimen, which was recently approved in Japan and is under review in Europe, the company said.

Biogen said it is planning to resubmit the application for approval using readily available information.