In the following video, Motley Fool health-care analyst David Williamson discusses Elan's (UNKNOWN:ELN.DL) sale of the rights to its MS treatment drug Tysabri to Biogen Idec (NASDAQ:BIIB) for $3.25 billion. This leaves Elan not only with a huge pile of cash and a nice revenue stream coming from the royalties of sales of the drug, but it has also drawn the interest of the privately held firm Royalty Pharma, which specializes in acquiring companies with intellectual-property revenue streams. David tells us what this could mean for Elan investors as a possible M&A deal could be getting closer, and what we will need to watch for from Elan, to know whether Royalty will remain interested.

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