Facing concerns about his own family history of Alzheimer's, CNN chief medical correspondent Dr. Sanjay Gupta visits preventive neurologist Dr. Richard Isaacson to have his own risk for dementia assessed in the CNN documentary "The Last Alzheimer's Patient." Watch the full documentary on CNN's "The Whole Story" premiering on May 19 at 8p ET/PT and streaming on MAX on June 18. | CNN