Shares of Vertex Pharmaceuticals Inc. /zigman2/quotes/202259802/composite VRTX +0.60% tumbled 13.8% in premarket trading Friday, enough to pace the S&P 500's /zigman2/quotes/210599714/realtime SPX -0.54% early decliners, after the biotechnology company released what was seen as disappointing data on its treatment for people with alpha-1 antitrypsin deficiency (AATD), which can lead to liver and lung disease. The stock was on track to open at the lowest price seen during regular-session hours since October 2019. The company said late Thursday that the Phase 2 trial of VX-864 mets its primary endpoint , showing a mean increase of 2.2 to 2.3 micromolar fAAT levels across the dose groups compared with placebo. Analyst Cory Kasimov at J.P. Morgan reiterated his overweight rating but cut his stock price target to $245 from $279, saying the trials results were "clearly" a setback. "Management is adamant that this is actually a step in the right direction for the program," Kasimov wrote. "We doubt [Wall Street] will agree." Stifel Nicolaus's Paul Matteis cut his stock price target to $244 from $277: "The announcement of modest AAT increases for VX-864, despite what looked like great data in animals, makes it difficult for us to garner conviction that futures compounds will perform materially better." The stock has lost 8.3% year to date, while the S&P 500 has climbed 12.9%.