This is the first in a series, "Inside Alzheimer's," about the experience of being diagnosed with early-onset Alzheimer's disease.

In 2009, 59-year-old Greg O'Brien was a successful journalist and writer living in Cape Cod. He was healthy and happy — he exercised every day, made a good living, spent time with his three children and wife.

But he had also started to notice changes in himself. He was forgetting things, and his judgment sometimes seemed to fail him. Meanwhile, his own mother was dying of Alzheimer's disease.

And that year, he was diagnosed as well.

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