(Adds analyst comment, share movement)
By Tamara Mathias
Sept 5 (Reuters) - Shares of ProQR Therapeutics NV surged 70 percent in premarket trading on Tuesday after an interim analysis of an early-stage trial showed that its experimental treatment for a rare form of childhood blindness improved vision.
The Dutch drug developer said it would now stop enrollments for the small study and progress to a mid-stage trial, which is expected to start in the first half of 2019.
The trial tested ProQR's RNA-based drug, QR-110, in 10 patients with a certain genetic mutation that causes an eye disorder called Leber's congenital amaurosis 10.
There are no approved treatments for the condition that primarily affects the retina and leads to severe visual impairment, beginning in infancy.
There are at least 2,000 patients in Europe and the United States with the specific mutation, according to the company's estimates.
After three months of treatment, about 60 percent of subjects showed a clinically meaningful response with improvements in vision and the ability to navigate, ProQR said.
The data show a "rapid and sustained benefit on every metric of vision assessed," JMP Securities analyst Liisa Bayko said.
Bayko said the market is worth over $700 million and the only other potential competitor is the gene-editing treatment approach from Editas Medicine Inc.
She said QR-110 now has a 60 percent probability of success, a huge jump from her previous estimate of 20 percent, and notes that the drug is likely to be launched in the United States in 2021, a year earlier than previously estimated.
"These results are very encouraging for our broader pipeline," Chief Executive Officer Daniel de Boer told Reuters, adding that the company was testing other drugs with similar mechanism.
ProQR is developing treatments for other rare eye diseases, including Usher syndrome and Stargardt's disease.
De Boer said the company was not planning to seek partners to develop the drug, QR-110.
ProQR is separately testing treatments for lung disease cystic fibrosis and skin disorder dystrophic epidermolysis bullosa.
The company's shares were trading at $13.50, on track to open at a near three-year high. Shares have more than doubled since the beginning of the year.
Reporting by Tamara Mathias in Bengaluru; Editing by Anil D'Silva and Sriraj Kalluvila