As world populations continue to age, the incidence of very common, ultimately fatal neurodegenerative diseases (some of medicine’s most puzzling illnesses) will increase exponentially. explores the diverse impacts and intense meanings of genetic diagnoses for patients suffering from such diseases, and for their family caregivers and clinicians. Through richly-textured, often heart-wrenching longitudinal case studies, reveals how extremely difficult it can be for patients to obtain a definitive diagnosis for the cause of their symptoms, even with genetic testing; how, with or without definitive diagnoses, patients and family caregivers strive to come to terms with their situations; and how they are aided (or not) in these endeavors by their doctors. The analysis is framed by increasingly sharp social debate over the consequences of decoding the human genome — and the impact of genetic technology on our lives.