Xenon Pharmaceuticals triggered a sharp sell-off after reporting adverse events in trials evaluating azetukalner, a treatment candidate for depression and bipolar disorder. The decision to voluntarily pause enrollment sent shares down to $42.35 in after-hours trading, reflecting investor anxiety over the drug's safety profile.

Conversely, Ultragenyx Pharmaceutical secured a significant victory as the Food and Drug Administration approved its therapy, Fayuvi, for children suffering from Sanfilippo syndrome type A. The positive regulatory news drove the stock up 13% to $14.50 during regular hours, with an additional 1.7% gain following the announcement. Separately, BRT Apartments bolstered its market position by authorizing a $10 million expansion of its stock-buyback program, pushing shares to $14.22 in late trading.