announcer: actor, scholar, athlete and activist, paul robeson used his acting ability to advance racialore at the... >> stahl: alzheimer's disease is the sixth leading cause of death in the united states. more than five million americans have alzheimer's right now, and given the aging baby boomer population, that number is projected to nearly triple by mid-century. yet unlike many other leading killers, there is no effective treatment. an alzheimer's diagnosis is essentially a prescription for a slow descent into oblivion-- an inexorable loss of the memories, spatial skills, and ability to think that make us who we are. early-onset alzheimer's patients, like the hundreds of family members in colombia, are a tiny fraction of the whole, but to scientists, they could be everything-- because they are offering researchers something they have never had before-- a way to test whether intervening, years before people start having symptoms, might halt the disease in its tracks. answers are still years away, but with more than 1,000 americans developing alzheimer's every day, a way to prevent it