Adding an investigational drug to conventional lipid-lowering drugs decreased “bad” cholesterol by nearly 50 percent among patients with a rare, inherited disease that causes high cholesterol and heart attacks as early as patients’ teenage years, according to results of a clinical trial.

Tarrytown, New York-based Regeneron Pharmaceuticals said Wednesday that topline results of the Phase III ELIPSE study of evinacumab added to cholesterol drugs showed an average 49 percent reduction of cholesterol in homozygous familial hypercholesterolemia (HoFH), compared with cholesterol drugs alone among the placebo group. Side effects more common among patients taking the drug included influenza-like illness and rhinorrhea.

The company plans to submit data to the Food and Drug Administration next year, and the drug has Breakthrough Therapy designation.

HoFH is a rare, genetic disease affecting about 1,300 people in the U.S. ELIPSE is enrolling 65 patients, randomized to receive evinacumab or placebo. Patients entering the study had an average level of “bad” LDL cholesterol of 255mg per deciliter of blood despite treatment with other drugs like statins, PCSK9 inhibitors, ezetimibe and other therapies like LDL apheresis.

“Currently, HoFH patients face limited choices in reducing their LDL cholesterol, including therapies that are time-consuming like LDL apheresis, or that may have side effect concerns,” Regeneron President George Yancopoulos said in a statement.

In a note to investors Wednesday, Cowen analyst Yaron Werber wrote that a key question now is the drug’s pricing, given that Amgen’s Repatha (evolocumab) is already approved for HoFH and carries a $5,850 per year list price, positioning evinacumab as an option for patients who have failed Repatha and statins. He noted that the evinacumab data are incrementally better than Repatha’s, with patients taking that drug still likely to have LDL cholesterol levels in the 250mg range.

While the drug is attractive, Werber wrote that a key question will be what payers are willing to pay for the segment of patients who take it. All in all, it represents a potential market worth $400 million-$800 million in the U.S. and Europe, whose HoFH population is of comparable size.

In addition to HoFH, Repatha is also approved for reducing the risk of certain cardiovascular events and strokes in patients with established cardiovascular disease and for primary hyperlipidemia.

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