A 5-Year, Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study to Evaluate the Effects of Two Amyloid Lowering Agents, CAD106 and a BACE 1 Inhibitor, on Postponing Cognitive Decline in Cognitively Unimpaired APOE4 Homozygotes Elderly Subjects at Risk for the Onset of Clinical Symptoms due to Alzheimer Disease.