Editor’s Note: We may have a new, extremely reliable test for Alzheimer’s disease. On Tuesday, a study published in the Annals of Neurology suggested that a spinal tap can detect, with nearly perfect accuracy, development of Alzheimer’s years before the symptoms start to appear. But since there’s no cure for Alzheimer's, what should Americans, as a society and individuals, do with this test? Who should get it? And when? We put those questions to Jonathan D. Moreno, a highly respected bioethicist at the University of Pennsylvania and author, most recently, of Progress in Bioethics.