Shares of Alnylam Pharmaceuticals Inc. soared to an all-time high price Monday after the drug developer said it will receive a $700 million investment from the Genzyme unit of French pharmaceutical giant Sanofi as part of an expanded collaboration.

Alnylam, which is based in Cambridge, Mass., said the investment amounts to a price of approximately $80 per share and will give Genzyme a 12 percent stake in Alnylam. That per-share price represents a premium of about 21 percent to Alnylam's closing price of $66.21 on Friday.

The companies said they will expand their agreement to develop and sell treatments for rare genetic diseases. They started teaming up in 2012 to develop Alnylam's lead product, patisiran, which is in late-stage clinical testing as a possible treatment for transthyretin-familial amyloid polyneuropathy, a life-threatening disease that damages the nervous system.

Alnylam said in November that the U.S. Food and Drug Administration gave patisiran a fast-track designation, which aims to speed up the review of drugs that treat serious medical conditions and fill an unmet medical need.

Genzyme will receive rights to sell patisiran in all territories outside North America and Western Europe under the expanded agreement. Genzyme also receives rights to worldwide sales of three products currently being developed by Alnylam, which has no drugs on the market.

Alnylam, in turn, will receive funding for research and development. It also could receive milestone payments and royalties from the agreement.

Alnylam also announced on Sunday that it will pay another pharmaceutical giant, Merck and Co., $175 million upfront to buy its Sirna Therapeutics unit. That price entails a $25 million cash payment and $150 million in Alnylam common stock shares. Merck also could receive more than $100 million in milestone payments and royalties.

Shares of Alnylam jumped nearly 60 percent, or $39.39, to $105.60 Monday in late morning trading. The stock had hit a new all-time high of $112.57 earlier in the trading session, according to FactSet.

That share price more than tripled in 2013 before closing the year at $64.30.