(Adds drug price, details, share price)
By Tamara Mathias
Aug 10 (Reuters) - Alnylam Pharmaceuticals Inc's drug for a rare hereditary disease won U.S. regulatory approval on Friday, becoming the first approved treatment from a new class of medicines that use gene silencing technology.
Onpattro, also known as patisiran, will have an annual U.S. list price of $450,000 for the average patient, the company said. The drug, which is dosed based on patient weight, was approved to treat polyneuropathy in patients with hereditary ATTR amyloidosis, a potentially fatal condition that affects an estimated 50,000 people worldwide.
Patients with the disease have a genetic mutation that prevents a type of protein from keeping its normal structure, instead causing it to fold into an incorrect shape and accumulate in the heart, nerves and other organs. This leads to loss of sensation, heart issues, eye, kidney and thyroid diseases.
Polyneuropathy, a symptom of the disease, is the simultaneous malfunction of nerves resulting in tingling, numbness and kidney dysfunction.
After taking into account mandatory government discounts, Onpattro will have an average net price of $345,000, Alnylam said.
The company also said it has reached "value-based agreements" with leading health insurers, including Harvard Pilgrim Health Care. Under such agreements, Alnylam would be paid based on the ability of the drug to deliver outcomes in the real world setting comparable to those seen in clinical trials.
Using RNA interference (RNAi), a Nobel prize-winning mechanism hailed as a breakthrough in the 1990s, Alnylam's patisiran targets and "silences" specific genetic material, which helps block the production of the deadly protein.
"We are welcoming in an entire new class of medicines," Alnylam's President Barry Greene said in an interview ahead of the FDA's decision. "Over time, RNAi therapeutics will be incredibly impactful over a wide range of diseases."
Other companies developing RNAi treatments include Ionis Pharmaceuticals Inc and Arbutus Biopharma Corp.
Alnylam plans to retain the global commercialization rights to Onpattro, Greene said.
The drug has already received a positive opinion from European regulators and Alnylam expects approval in September.
Alnylam is also developing other RNAi drugs to treat a range of conditions, including high cholesterol and genetic bleeding disorder hemophilia.
Shares of Alnylam, which closed 3 percent higher in regular trading, were down $4.37, or 4 percent, at $93 after hours on Nasdaq.
Reporting by Tamara Mathias and Manas Mishra in Bengaluru; Additional reporting by Deena Beasley in Los Angeles; Editing by Sai Sachin Ravikumar and Diane Craft