Since 2008, Shire PLC 's market cap has nearly doubled ($8.3 billion to $16 billion) and its employee count has grown from 1,600 to roughly 4,300. Analysts say the U.K. company is on track to deliver its revenue guidance of 15% compound annual growth rate (CAGR) through 2015 – far above the expected anemic performance of most pharmaceutical companies.

Big pharmas from Pfizer to GlaxoSmithKline are expanding their initiatives in niche disease areas, but if Sanofi-Aventis acquires Genzyme as it hopes, the French drug maker could soon emerge as an orphan drug leader

If successful, Sanofi-Aventis' attempt to acquire Genzyme would catapult the company into the orphan drug business, marking Big Pharma's most aggressive strategy in the space to date.