Deerfield buys 42% of Prosensa float, shares jump Shares of Prosensa (RNA +8.2%) spike after Deerfield Management discloses it has taken a 3.22M share position in the company, representing 42.5% of the float and 11.1% of shares outstanding. (SC 13G)As of Sept. 13, 1M shares had been sold short, nearly triple the interest on Aug. 30