Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Protalix BioTherapeutics (NYSE: PLX) sank more than 20% in intraday trading Friday after the company said the Food and Drug Administration is asking for more information about its potential Gaucher disease drug taliglucerase alfa before it can move to approve the treatment.

So what: Gaucher disease drugs marketed by Genzyme (Nasdaq: GENZ) (Cerezyme) and Shire (Vpriv) produced sales last year of $719.6 million and $143 million, respectively, so an approval for the small-cap Protalix would obviously be a big deal. Unfortunately, the FDA won't consider approving taliglucerase until it receives more data on things like the drug's chemistry and manufacturing process, triggering Protalix's largest one-day stock price decline in three years.

Now what: Today's 20%-plus sell-off looks to be a tad overdone. Protalix said that it plans to work closely with its gorilla co-developer Pfizer (NYSE: PFE) to get all of the FDA's questions answered and that it expects to do it in fairly short order. The FDA doesn't seem to have any major safety issues with taliglucerase, so for now, at least, the delay looks like a small setback rather than a crippling blow.

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Fool contributor Brian Pacampara owns no position in any of the companies mentioned. Pfizer is a Motley Fool Inside Value pick. Try any of our Foolish newsletter services free for 30 days.

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