** Shares of Biogen BIIB.O rise 1.1% to $198.02 premarket

** The drugmaker says the U.S. Food and Drug Administration granted breakthrough therapy designation to its experimental drug salanersen for spinal muscular atrophy (SMA)

** The breakthrough therapy tag is meant to speed up development and review of drugs to treat serious conditions or those with unmet medical needs

** SMA is a rare genetic disease that causes severe muscle weakness and can be fatal

** The tag was based on early stage data showing that drug may offer substantial improvement over currently available therapies - BIIB

** Up to last close, stock up 11.4% YTD