Spark Therapeutics Inc said its experimental gene therapy helped improve vision in patients with a type of inherited eye disorder in a late-stage study, sending its shares up more than 50 percent in premarket trading.

The drug developer said its lead drug, SPK-RPE65, met the goals of improving vision and sensitivity to light in patients previously at the risk of total blindness.

SPK-RPE65 is a form of gene therapy, a treatment which aims to insert corrective genes into malfunctioning cells.

Spark, whose shares were trading at $69.51 before the opening bell, said it would file for marketing approval in the United States in 2016.

Mutations in the RPE65 gene lead to a range of visual impairments. The gene is present in a cell layer just outside the retina.

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The drug could be worth about $65 per share to Spark for this specific condition, Cowen & Co analysts wrote in a note last week.

Shares of the company have almost doubled since its IPO debut on Jan. 30.

The study tested the drug in 31 patients with inherited retinal dystrophies (IRDs), a broad group of hereditary disorders affecting the retina.

Although gene therapy has been touted as a one-time cure for intractable and expensive-to-treat diseases, it has been dogged by a series of disappointments and safety concerns in its more than 20 years of research.

However, investor interest in the field has grown this year, with Bluebird Bio Inc, UniQure NV and Spark all staging successful Nasdaq debuts.

There were no serious adverse events or harmful immune responses observed in the trial, Spark said on Monday.

The company's pipeline also carries experimental treatments for other conditions including blood disorders and neurodegenerative diseases.