Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Alnylam Pharmaceuticals (NASDAQ:ALNY), a biopharmaceutical company focused on developing RNAi-based therapeutics, rallied as much as 70% after announcing a sizable investment by Sanofi's (NYSE:SNY) Genzyme.

So what: According to the terms of this collaboration/investment, Sanofi will pay Alnylam $700 million in order to gain expanded rights to familial amyloidotic polyneuropathy drug patisiran globally, except for North America and Western Europe. In addition, Sanofi will gain global rights to co-develop and co-commercialize ALN-TTRsc, a mid-stage drug for familial amyloid cardiomyopathy, as well as two additional products in early clinical trials. As with patisiran, Alnylam maintains licensing rights in North America and Western Europe. Finally, Sanofi will have the option until at least 2020 to develop and commercialize rare genetic disease drugs from Alynlam's pipeline globally, minus North American and Western Europe. With its investment, Sanofi becomes a 12% stakeholder in Alnylam, with its purchase price being $80/share, or a 27% premium to Friday's close.

Now what: This is one of those head-scratchers, because the deal seems to make a lot of sense for Sanofi which can utilize Alnylam's RNAi technology platform to treat genetic diseases in the Asia-Pacific region, while not really providing the clearest of catalysts for Alnylam. Yes, the purchase of 12% of Alnylam's outstanding shares at a 27% premium is a catalyst in and of itself, and it could speak to the idea of Sanofi eventually buying Alnylam if their collaboration produces solid results. Unfortunately, at a valuation now topping $6 billion, I'd like to see its multiple trials start to turn into marketable and FDA-approved compounds. Until a number of these experimental compounds reach later-stage studies, I have a hard time seeing how investors are going to squeeze any more upside out of Alnylam.

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Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

The Motley Fool recommends Alnylam Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.