What: After Amicus Therapeutics (NASDAQ:FOLD) reported new phase 3 data for its lead product candidate, its stock jumped higher by 10% at 3:00 p.m. ET today.

So what: The clinical-stage drugmaker is awaiting an EU decision on the approval of Galafold, a therapy for use in treating Fabry disease, a rare genetic condition.

Currently, Fabry disease is treated in the EU with Shire's (NASDAQ: SHPG) enzyme replacement therapy Replagel, a six-figure-per-year therapy that pulled in about $440 million in sales last year.

In phase 3 trials, patients who hadn't been treated with an ERT like Replagel saw a statistically significant improvement in podocytes, or cells in the kidney that help filter blood and that build up in Fabry disease patients.

Amicus Therapeutics also reported that Galafold's effects on kidney and cardiac function persisted in a subset of patients who switched over to its 19- to 30-month extension study.

Now what: Following its admission last year that its timeline for a Food and Drug Administration application and approval is uncertain, Amicus Therapeutics shares have tumbled. However, given Shire's success, an approval in the EU could still be significant. Furthermore, because Galafold works differently than Replagel, it could eventually be used alongside it as part of a standard of care, rather than instead of it, and that could boost its market opportunity.

Given that Amicus Therapeutics' market cap is just $770 million, that market opportunity is intriguing. However, the U.S. market is a big question mark and therefore, until an EU decision on Galafold and a timeline for its potential use in America is announced, buyers should approach this company cautiously. 

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.