 Shares of biotech AC Immune SA ACIU, -9.21 slid 15 in premarket trade Thursday, after the company said a a trial of a treatment for Alzheimers disease failed to slow or prevent cognitive decline in patients with a specific genetic mutation that causes early-onset disease. The trial involved 252 people who are members of the worlds biggest extended family with Autosomal Dominant Alzheimers Disease, or ADAD, in Colombia. 