Starting in his early 50s, Lou Bordisso Jr. knew something was wrong.

One time, he got lost in a Macy's store in San Francisco and couldn't find his way out. Another time, expected in a meeting, he rode confused from floor to floor in one Financial District skyscraper, then the one next door.

"I could not for the life of me find the conference room," said Bordisso. "Then one day, I couldn't remember how to log in to my computer. That was the beginning."

At 57, the American Catholic Diocese of California priest should be in the prime of his life – but last year, he was diagnosed with dementia related to Alzheimer's disease.

There's good reason we think of Alzheimer's as a problem of old age: Age is the degenerative brain disease's only known risk factor. Fully 90 percent of people with Alzheimer's are 75 and older, experts say, and nearly half of people over 85 have it.

Even so, according to the Alzheimer's Association, a small sliver of the diagnosed – up to 5 percent – haven't yet seen their 65th birthdays. That means 200,000 Americans younger than 65, including 19,200 Californians, have the disease.

The early-onset form of Alzheimer's is little understood. Experts know that for a small number of people whose memory loss begins in their 30s and 40s, genetic factors play a role. But why do other people in their 50s and early 60s get the disease?

Researchers don't know.

"It's a less common age to have this disease," said Judy Filippoff of the Alzheimer's Association of Northern California. "At 65 and younger, most people don't expect this diagnosis. They have many responsibilities, and they haven't slowed down, either physically or mentally.

"And now they have to change their life in ways they didn't imagine. It can be quite a shock."

Much too early, people diagnosed with early-onset Alzheimer's lose their past as well as their future. The disease is both progressive and fatal and has no known cure.

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