A new theory for Alzheimer’s disease is emerging, and at least one company is taking advantage of the new thinking with drugs in human trials — The mood among the more than 3,000 researchers who gathered in Lisbon, Portugal, at the end of March for the 14th International Conference on Alzheimer’s and Parkinson’s Diseases was downbeat. Just a few days earlier, Biogen, the Cambridge, Massachusetts-based biotech company, and Japanese pharmaceutical company Eisai Co had jointly announced…