Sarepta Therapeutics Inc.’s miss on a key phase II ambulatory endpoint in its Duchenne muscular dystrophy (DMD) trial may have been caused by a dramatic disparity in functional ability at baseline among older vs. younger patients afflicted with the progressively worsening disorder. In any case, Wall Street had knives out, carving 51% of the value away from shares (NASDAQ:SRPT) of the Cambridge, Mass.-based firm, which closed at $82.29, a loss of $86.66, or 51%.