Fool me once, shame on you; fool me twice, shame on me; fool me thrice, hit the sell button.

OK, so I just made up that last part, but yesterday, Protalix BioTherapeutics' (AMEX: PLX) investors seemed to be following the mantra as they sent the stock down 13% following the company's announcement that the Food and Drug Administration had pushed back the decision on whether to approve taliglucerase alfa by three months.

You'll recall -- or maybe not, considering how long ago it was -- that almost two years ago, the FDA asked Protalix and marketing partner Pfizer (NYSE: PFE) for more data on the manufacturing process for taliglucerase alfa. After it gathered the data and submitted it the FDA, the agency said it wasn't good enough and asked for more information.

After the duo submitted a second marketing application, the FDA set a goal of making an approval decision by Feb. 1. Unfortunately, the agency asked for more clinical data during the second review, and decided it needed until May 1 to make a decision.

Orphan drugs have become a lucrative business as BioMarin Pharmaceutical (Nasdaq: BMRN) and Shire (Nasdaq: SHPGY) have shown. They were the driving force for Sanofi (NYSE: SNY) to buy Genzyme. But this is getting a little ridiculous, and I don't blame investors for moving on.

Protalix uses plant cells to manufacture the drug. The novelty has its advantages, lower costs among others, but the novelty seems to be coming with added scrutiny from the FDA. Since the manufacturing side tends to be a black box for investors, it's difficult to assess the risk of another rejection.

The delay could be nothing. It could be the last one. This could be an excellent entry point. But "coulds" aren't very reassuring. Unfortunately, there's just no way to know if Protalix has finally submitted enough data to convince the FDA to approve taliglucerase alfa.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.