BUZZ-Prosensa Holding NV: To be bought by BioMarin for about $840 mln
** Dutch drug developer's shares up about 65 pct at $18.87 premarket; set to open at a more than one-year high
** Company's shares one of the top percentage gainers among Nasdaq-listed stocks in premarket trading
** BioMarin Pharmaceuticals Inc to buy Prosensa for about $840 million including milestone payments
** Deal will give BioMarin worldwide rights to several orphan-drug candidates including drisapersen, which is being developed to treat Duchenne muscular dystrophy, a rare muscle degeneration disease
** Shares of rival Sarepta Therapeutics Inc, which is also developing a drug to treat DMD, up about 13 pct
** Up to Friday's close, Prosensa's shares had more than doubled this year
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