How much is enough?

FDA Commissioner Robert Califf boiled the myriad conflicts over whether to grant accelerated approval to Sarepta Therapeutics Inc.'s Exondys 51 eteplirsen down to one fundamental scientific dispute.

It all comes down to a disagreement between CDER Director Janet Woodcock, who granted the approval, and Office of Drug Evaluation I Director Ellis Unger, who appealed her decision, about whether the quantity of dystrophin the drug produces is reasonably likely to predict clinical benefit...