A medicine Stealth Biotherapeutics Inc. has been developing for the potential treatment of primary mitochondrial myopathy (PMM) missed the co-primary endpoints of a key phase III trial, sending company shares (NASDAQ:MITO) down 65.9% to close at $4.75 on Friday.

With Alexion Pharmaceuticals Inc.'s acquisition of Achillion Pharmaceuticals Inc. for about $930 million up front, Alexion expands and diversifies its pipeline into familiar territory – treating complement-mediated diseases. Blue Bell, Pa.-based Achillion is developing oral, small-molecule factor D inhibitors for treating complement alternative pathway-mediated rare diseases, including paroxysmal nocturnal hemoglobinuria and C3 glomerulopathy.

Alexion Pharmaceuticals Inc. and Stealth Biotherapeutics Corp. reached a deal for an option to co-develop and commercialize elamipretide for mitochondrial diseases.

Approval of Alexion Pharmaceutical Inc.'s Soliris (eculizumab) injection to treat neuromyelitis optica spectrum disorder (NMOSD) in adult patients who are anti-aquaporin-4 (AQP4) antibody positive makes it the first and only FDA-approved treatment. It's also one of the most expensive treatments in the world, making it vulnerable to off-label use and the eventual creep of biosimilars into the market.