Could Someone Run the Country With Alzheimer's Disease?

Jan. 17, 2011— -- Six years after finishing his second term as the president of the United States, Ronald Reagan was diagnosed with Alzheimer's -- a devastating neurological disease that impairs memory, judgment and reasoning. But the former president's son, Ron Reagan, says he saw the early signs of Alzheimer's while his father was still in office.

"It wasn't anything that obvious. It wasn't like, 'Oh my God, he doesn't remember he's president,' Ron Reagan said in an exclusive interview with ABC News. "It was just, I had an inkling that there might be something going on."

Ron Reagan recounts what he calls the early signs in his new book, "My Father at 100: A Memoir."

Alzheimer's disease, which is estimated to affect up to 5.1 million people in the U.S. according to the National Institute on Aging, is an irreversible and progressive brain disease that affects a person's ability to carry out the simplest tasks of daily living. But subtler changes in memory and mood can signal the disease's early stages.

"Most commonly people complain of short term memory issues," said Dr. Gary Small, director of the University of California, Los Angeles Center on Aging. Forgetting plans and having trouble remembering names or words -- the so-called 'tip of the tongue' phenomenon -- are common early symptoms. And although they might not interfere with someone's job in the beginning, they will as they worsen.

"If it really is early Alzheimer's and it progresses over the years, the person's memory and cognitive ability become more impaired," said Dr. David Loewenstein, chief of psychiatry at the University of Miami. This can affect a person's attention to detail and their ability to keep track of situations and react accordingly -- all of which affect a person's ability to do their job. For Ronald Reagan, the job was running the country.