Amicus Therapeutics (FOLD - Get Report) is facing an extended delay of at least two years before a U.S. approval filing for the Fabry disease drug Galafold will be ready.

The U.S. Food and Drug Administration turned down Amicus' request to seek accelerated approval for Galafold based on an existing kidney biomarker data. Instead, the agency instructed Amicus to conduct another clinical trial to collect new gastrointestinal symptom data in Fabry patients, the company said Monday.

Shares of Amicus fell 28% to $5.98 in Monday's after-hours trading session.

Amicus plans to start the new study in 2017 but doesn't expect to have the clinical data until 2019.

"While we believe that the totality of the data from our studies with migalastat [Galafold] support the submission of a new drug application today, we acknowledge the FDA's position that accelerated approval based on kidney GL-3 reduction is not currently an option," said Amicus CEO John Crowley, in a statement.

"We have thus defined a plan to collect additional GI data to support full approval for migalastat that we believe is feasible in a reasonable amount of time and with a high likelihood of success based on positive GI data generated in our previous Phase 3 Study 011."

European regulators approved Galafold in May based on the clinical data FDA found insufficient.

Fabry is an inherited disease affecting about 10,000 people worldwide in which a genetic mutation stops an enzyme from breaking down a fatty substance known as globotriaosylceramide, or GL3. The buildup of GL3 in blood vessels throughout the body causes severe damage to kidneys, heart, brain and other organ systems.

Sanofi (SNY - Get Report) and Shire  (SHPG)  market competing therapies for Fabry disease.

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