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What's happening?
Shares of Alnylam Pharmaceuticals (NASDAQ:ALNY), a developer of drugs based on RNA interference, surged 21% after the company reported its six-month clinical data for its midstage open-label extension study involving patisiran as a treatment for transthyretin-medicated amyloidosis in patients with familial amyloidotic polyneuropathy, or FAP.

Why it's happening?
According to Alnylam's early-morning press release, presented at the American Neurological Association's annual meeting, there was a mean 0.95 decrease in the modified Neuropathy Impairment Score at the six-month mark in the 19 currently evaluable patients. To add some context to these figures, historical data would suggest over this time frame that FAP patients would normally progress seven to 10 points higher on the Neuropathy Impairment Score. In this case, its drop of nearly a point demonstrates early but encouraging efficacy in slowing disease progression.

Alnylam also notes that patisiran delivered a mean serum transthyretin reduction at the targeted 80% level for more than nine months, with the knockdown between doses just shy of 90%. No serious adverse events have been reported, and no patients had discontinued taking the drug at the time of the analysis.