If orphan drugs and rare diseases were a theme of 2013's biotech bull market, then today's $700 million deal between Alnylam (NASDAQ:ALNY) and Sanofi (NASDAQ:SNY) is a sign it isn't slowing down anytime soon.
 
Alynlam wasn't just on the receiving end. It went out and acquired fellow RNAi specialist Sirna Therapeutics from Merck (NYSE:MRK) for just a fraction of what the Big Pharma paid for it in 2006.

In this video, Motley Fool health-care analyst David Williamson discusses the specifics of the deals, what Sanofi is gaining, why the market loves Alnylam, and why 2015, with half a dozen proof-of-concept trials reporting, will be a big year for the stock.