Orphan drugs, treatments for rare and ultra-rare diseases that have traditionally lacked reliable medicines, have become big business in biotech and pharmaceuticals. Alexion Pharmaceuticals' Soliris might be the most well-known example of a single orphan drug transforming a company from developing firm to biotech powerhouse, as Soliris, a treatment for rare blood disorders, raked in more than $1.3 billion in revenue last year and is set for even greater sums in the future.

Other companies are hoping to harness the power of orphan drugs, and two biotech companies in the thick of the race are Vertex Pharmaceuticals (NASDAQ:VRTX) and BioMarin (NASDAQ:BMRN). Vertex has pushed forward behind Kalydeco, its up-and-coming treatment for cystic fibrosis-related mutations, while BioMarin's hoping to turn recent FDA and European approval for its Morquio-A syndrome therapy Vimizim into strong sales in the near future.

However, both of these stocks have slumped over the past year despite the two companies looking forward to what their orphan drugs can deliver. Will either of these stocks bounce back, and which one's the best to keep your eye on? Find out in the video below, as Motley Fool contributor Dan Carroll takes you through what's powering these two biotech stocks -- and whether either can turn things around for investors.

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Dan Carroll has no position in any stocks mentioned. The Motley Fool recommends BioMarin Pharmaceutical and Vertex 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.