Amicus Therapeutics on Wednesday disclosed new data from its Phase 2 trial of Pompe disease therapy AT-GAA that show continued improvement in patients’ walking ability, strength and breathing ability after two years of treatment. The company’s shares, however, fell by as much as 10% amid broader market turmoil.The updated data, presented at a medical meeting, include for the first time a group of patients who were previously treated with enzyme replacement therapy for an average of 10 years. Five of six patients saw some motor improvement by six months after switching to Amicus’ drug.Continued improvement in treated patients bodes well for Amicus’ Phase 3 study, wrote Cantor Fitzgerald analyst Elemer Piros. That trial, which the Food and Drug Administration asked Amicus to conduct before filing for approval, compares treatment with AT-GAA to Sanofi’s enzyme replacement therapy Lumizyme. Recruitment should complete by the end of 2019, and results are due by early 2021.

If all had gone according to Amicus’ plans, AT-GAA might already be on the market now to treat patients with Pompe disease, a condition in which an enzyme shortage leads to progressive declines in muscle strength and respiratory capacity.

Typically, patients are treated with enzyme replacement therapy like Lumizyme (alglucosidase alfa).

The FDA was not as accepting of Amicus’ application as it has been with some other rare disease drugs, asking the company for data from its Phase 3 PROPEL trial which had been planned to confirm AT-GAA’s efficacy.

While Amicus awaits data from PROPEL, it is continuing to monitor patients in its Phase 1/2 study. This tested AT-GAA, which combines a new enzyme-replacement therapy with a chaperone drug to improve delivery, in patients with different characteristics, from newly diagnosed patients to those who have lost the ability to walk.

Wednesday’s presentation at the World Muscle Society updates the data through 24 months of treatment for three of four studied cohorts. Patients who switched from Lumizume to AT-GAA and still had the ability to walk improved their six-minute walk tests by 36 meters, or 9%, while those who had never taken Lumizyme improved by 61 meters, or 15%.

The six-minute walk test is the primary measure in the Phase 3 trial.

The presentation also include a cohort of ambulatory patients who had been recruited because they have been on Lumizyme for more than seven years. At six months, they improved on the six-minute talk test by 24 meters, or 9%.

Speaking at an investor conference Wednesday, Amicus CEO John Crowley said the walking data show that AT-GAA can “not only stop the progression of disease but also reverse it.”

A fourth group of patients who had taken Lumizyme but had lost their ability to walk saw improvements in upper body strength.

SVB Leerink analyst Joseph Schwartz agreed with Piros’ assessment, writing in an Oct. 2 note to clients that the 24-month data “bolsters our confidence in [Amicus’] ongoing Phase 3 PROPEL study.”