Biogen (NASDAQ: BIIB) has enjoyed some good news lately. The spinal muscular atrophy drug that it licensed from Ionis Pharmaceuticals (NASDAQ: IONS) won U.S. regulatory approval in December, and the launch appears to be going well. The spin-off of its hemophilia business into a separate entity, Bioverativ (NASDAQ: BIVV), went without a hitch — and Bioverativ’s stock has racked up nice gains so far in 2017.