** Shares of gene therapy maker bluebird bio BLUE.O rise 50.5% to $4.98 premarket

** Bluebird bio says its board approved the revised merger deal with investment firms Carlyle CG.O and SK Capital Partners

** Under terms of the amended deal, bluebird stockholders can elect to get $5 per share in cash or the original offer of $3 per share in cash plus a contingent value right of $6.84 per share that is payable upon achievement of a net sales milestone

** New offer price of $5 represents a 51% premium to BLUE's last closing price

** "The amended offer price provides an alternative for stockholders who would prefer greater upfront cash consideration instead of the potential upside of the CVR", the cos say

** Up to last close, stock down 60.3% YTD

(Reporting by Sneha S K)

((Sneha.SK@thomsonreuters.com))