Alzheimer’s disease poses a huge threat to our health and our economy — more than 5 million Americans are estimated to currently have the disease. But it has been as good at evading treatment as just about any disease out there.For decades, scientists’ efforts in treating Alzheimer's have been focused on a protein in the brain called beta amyloid. Some think that the seeds of the disease’s destruction lie in the protein. But others in the field think that may be a dead end. Who is right?The Signal podcast is produced by Katie Hiler. Illustration by Molly Ferguson for STAT.