Protalix BioTherapeutics (AMEX: PLX) is up more than 40% this year as investors poured into the company ahead of its return trip in front of the Food and Drug Administration. The agency is scheduled to decide about its Gaucher disease treatment taliglucerase alpha on Tuesday, although that's more of a goal than a deadline. The drug is licensed to Pfizer (NYSE: PFE), but Protalix's stock has greater potential to move on the approval because of its smaller size.

Taliglucerase alpha was up for approval two years ago, but the decision was delayed because the FDA wanted more information on the manufacturing process for the drug, which is made in plant cells rather than the more traditional mammalian cells. Eventually, the FDA rejected the drug, requesting clinical data on the switchover trial and other information about how it tests the drug to make sure it's been produced correctly.

I hate these types of binary events. There are too many unknowns with manufacturing issues to feel confident about an approval. Discovery Laboratories (Nasdaq: DSCO), for instance, went through four rejections mainly for manufacturing issues before finally gaining approval of Surfaxin, its preventative for respiratory distress syndrome.

And it's not as if the FDA is likely to be lenient just because Gaucher disease is rare. The FDA turned down ViroPharma's (Nasdaq: VPHM) request to make Cinryze at a larger scale because it had additional questions about the technical process of the making the new formulation of the treatment for an orphan disease called hereditary angioedema. And last week, Shire Pharmaceuticals (Nasdaq: SHPGY) announced that the FDA had turned down the approval of the new manufacturing site for Vpriv, which also treats Gaucher disease.

Protalix says it's answered all the FDA's questions, and I have no reason to think otherwise. But investors have very little insight into what the FDA is thinking about the manufacturing issues. I hope taliglucerase alpha is approved, but given the unknowns, I don't see how it's worth placing a big bet on the agency's decision.

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