Alnylam Pharmaceuticals said on Wednesday it would halt development of an experimental therapy for a rare genetic condition that can cause heart failure, after a late-stage study showed that patients given the drug were more likely to die than patients treated with a placebo.
Alnylam shares fell more than 48 percent following the announcement and ended the day at $36.21 a share.
The drug, revusiran, was being developed for treating hereditary amyloidosis with cardiomyopathy, a condition in which amyloid plaque — similar to the substance found in the brains of Alzheimers' patients — collects in organs including the heart, where it can cause heart failure.
Alnylam specializes in a technology known as RNA interference (RNAi), which prevents genes from making their designated proteins. Revusiran was designed to target the gene involved in producing the abnormal protein which causes amyloidosis.
Amyloidosis is diagnosed in 6 to 10 Americans per million each year, according to the American Heart Association, though it is likely underdiagnosed.
Alnylam said study safety monitors recommended that the Phase III trial be suspended after patients on a previous study developed neuropathy, or nerve pain. Unblinded data subsequently "revealed an imbalance of mortality in the revusiran arm as compared to placebo."
The company said the decision does not affect its lead product patisiran, which is currently in Phase III development for treatment of amyloidosis with polyneuropathy, or any other Alnylam investigational RNAi therapeutic program.
Alnylam also said current data across its other programs, including a cholesterol-lowering drug partnered with The Medicines, do not show evidence of drug-related neuropathy.
Shares of The Medicines declined 8 percent to close at $35.33.
Alnylam last month halted development of an earlier-stage RNAi compound after observing elevated liver enzymes in healthy volunteers.