Rare-Disease Treatment from Alnylam Will Cost $450,000 a Year

Alnylam Pharmaceuticals Inc. won approval from the U.S. Food and Drug Administration for its first-of-a-kind treatment for a rare, often deadly nerve disease and plans to charge about $450,000 a year for the therapy.

Patients who have the condition, called hereditary transthyretin-mediated amyloidosis, or hATTR, will take the drug for the rest of their lives, racking up costs in the millions of dollars. After expected discounts in the U.S., Alnylam said in a statement that it expects the net cost for the drug to be about $345,000 a year.

Alnylam spent years developing the drug, called Onpattro, based on Nobel ...