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What happened? 
Rare disease focused Alexion Pharmaceuticals (NASDAQ:ALXN) shared good news today that Kanuma, its treatment for lysosomal acid lipase deficiency -- or LAL-D -- won FDA approval. 

LAL-D is an awful, ultra-rare genetic metabolic disease in which patients do not produce enough of the LAL enzyme, resulting in a huge buildup of cholesteryl esters and triglycerides in key organs. The disease eventually leads to multi-organ damage and even premature death. Up until today there was no approved therapy to treat the disease in the U.S.

To add more good news to the mix, the FDA once again issued a Rare Pediatric Disease Priority Review Voucher to Alexion, which allows the company to gain priority review for a drug down the road that otherwise would not qualify. The company also retains the options to sell the voucher on the open market, which it may want to do -- another voucher traded hands earlier this year for $350 million. 

Alexion is currently in the final stages of preparation and expects that Kanuma will become available for sale in early January.

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Does it matter?
Alexion investors are breathing a little easier today after securing this win -- let's not forget that back in September, the FDA announced that they were extending Kanuma's PDUFA date by 3 months. At the time, the FDA wanted to see additional data related to the drug's chemistry and manufacturing, stating that it needed more time to review the application. Everything appears to have progressed smoothly since then, and today's news has investors bidding up shares by over 5%.

Analysts are projecting that peak sales for Kanuma could eclipse $1 billion. If Kanuma can reach that level of sales volume, it will go a long way toward helping the company recoup the $8.4 billion that it spent on acquiring Synageva to get its hands on Kanuma in the first place.

Brian Feroldi has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. 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.