Sarepta shares dropped as much as 5.2 per cent on Monday amid volatile trading, while those of Replimune — another gene therapy group — fell as much as 15.1 per cent. Replimune has a drug pending approval before the FDA division Prasad oversees. The declines eroded some of the gains the stocks experienced following his departure.

The shares of biotech companies fell after news that ousted regulator Vinay Prasad is set to go back to the US Food and Drug Administration. Prasad had previously overruled his own scientific review staff and took a confrontational approach that critics said would stymie scientific innovation and slow drug approvals.