Samuel L. Jackson attends as many fundraisers for Alzheimer's disease as he can because he's convinced he'll be diagnosed with dementia before he dies.

The movie star fears he'll follow in the footsteps of so many relatives who have succumbed to the condition, which robs sufferers of their memories.

He says, "My grandfather had Alzheimer's, my maternal and paternal grandmothers had it, my mum died from it last year, her sister's got it. Because it's around me like that, I'm kind of waiting on that day where I walk in a room and don't know why I'm there.

"I'm going to do all I can to help people because of that."

And Jackson is also hoping to raise awareness about the disease by playing a 91-year-old man struggling to cope with Alzheimer's in a new film.

He tells Playboy, "The one old-guy story I want to do is a great book by Walter Mosley, The Last Days of Ptolemy Grey, about a 91-year-old guy with Alzheimer's who is told by a doctor that he can give him all his cognitive functions back, but he'll die in a week.

"He does it because he has some s**t he wants to get together."