Shares of Ionis Pharmaceuticals Inc. (NASDAQ:IONS) fell 21.7% to $43.59 on March 23 after its longtime partner, Roche Holding AG, decided to stop dosing the antisense oligonucleotide tominersen in a global phase III manifest Huntington's disease (HD) study. Roche subsidiary Genentech Inc. said the move was based on an independent data monitoring committee's preplanned assessment of the drug's risk-benefit profile.