Underwriters for Dicerna Pharmaceuticals Inc.'s IPO took the rare step of waiving a lockup period for the RNAi play - a move that could give some existing shareholders a free hand to immediately realize some of the massive returns they now enjoy.

Dicerna (NASDAQ:DRNA) raised $90 million on Jan. 29 through the sale of 6 million shares at $15, giving it a postmoney valuation of $294.4 million. The stock more than tripled in its trading debut on Jan. 30