LOS ANGELES (CBSLA.com) — The daughter of former President Ronald Reagan criticized actor Will Ferrell Thursday for agreeing to portray her father in an upcoming movie that highlights his battle with dementia.

In an open letter to Ferrell, Patty Davis wrote: “Perhaps you have managed to retain some ignorance about Alzheimer’s and other versions of dementia. Perhaps if you knew more, you would not find the subject humorous.”

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“Alzheimer’s is the ultimate pirate, pillaging a person’s life and leaving an empty landscape behind,” she continued. “It sweeps up entire families, forcing everyone to claw their way through overwhelming grief, confusion, helplessness, and anger.”

The letter goes on in detail to explain how Davis watched her father struggle with the disease for ten long years as he “reached for memories, for words, that were suddenly out of reach and [moved] farther away.”

“There was laughter in those years, but there was never humor,” she added.

At one point, Davis calls attention to her support group that runs twice a week, called Beyond Alzheimer’s, for caregivers and family members.

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She concludes the letter by challenging Ferrell to visit dementia facilities in hopes that he would not find anything comedic there.

On Wednesday, Variety announced Ferrell will star as Ronald Reagan in a movie called “Reagan,” set during the former Republican president’s second term in the White House.

The script centers on a fictional scenario in which Reagan falls ill to dementia and is convinced by an intern that he is an actor playing the president in a movie.

Ferrell’s upcoming role will not be his first try at playing a former president. He previously won acclaim for his George W. Bush impersonation on “Saturday Night Live.”

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The comedian is also slated to produce the film.