In 2008, Pam White began to write a biography of her late mother, Marian Williams Steele, a notable New England painter whose impressionist landscapes and portraits hang in several museums. Steele had died of Alzheimer’s disease and a year after White launched her project, she herself was diagnosed with early onset Alzheimer’s.

In “The Genius of Marian,” documentary filmmaker Banker White tells the story of his mother, and her struggle with Alzheimer’s disease. The film, which airs nationally for the first time on PBS’s POV on Sept. 8, works as both a tribute to Pam White and a poignant personal exploration of the impact Alzheimer’s disease can have on a single family – twice, in this case, involving successive generations of women.

At times, the movie is almost stressfully intimate.

That’s perhaps because Banker White hadn’t intended to make the documentary. In an interview Tuesday, he said the movie evolved from helping with his mother’s book project by creating a sort of a visual diary, and then became a way of allowing her to share her feelings about an illness she was reluctant to acknowledge, let alone discuss.

“So I didn’t think I would really share a lot of what went into this movie. But she felt better as I was doing it, and so did I,” Banker White said. His family also gave their blessing to the project, and reviewed it frame by frame before its premiere in the Tribeca Film Festival last year.

The documentary comes at a time of growing awareness of the heavy impact Alzheimer’s has on women. It’s well known that women are more likely to suffer from the disease in part because they live longer. But recent research also suggests that women may be at greater risk of Alzheimer’s because of gender-specific biological causes.

Women bear a heavier burden in other ways too. Earlier this year, the Alzheimer’s Association issued a report showing that women are also 2.5 times more likely to act as primary caregivers for dementia-stricken family members.

But the abstract dimensions of the disease pale against the unusually close look at the White family’s experience in “The Genius of Marian.” The documenary does not go into the science of Alzheimer’s or the demographics of an illness that is becoming more common as the U.S. population ages. It also assumes that viewers know that Alzheimer’s is an incurable disease that progressively destroys nerve cells in the brain.

Instead, the movie’s focus is relentlessly human as the camera shows the steady loss and intensifying anguish that follow in the path of Alzheimer’s disease. And yet it also speaks to the deep human bonds that give people the strength to care for their loved ones.

“I have already started really enjoying watching the early part of the movie and early footage because it kind of captures the spirit of my mom, which you can still see in her smile,” Banker White said in an interview Tuesday. “Just hearing her talk at length, and hearing her discuss her ideas at length, I really loved looking at that now. Because it’s amazing, because it’s not that long ago.”

Until her diagnosis, Pam White’s life was, in many ways, blessed. Like the storybook character Eloise, she grew up in a hotel her father owned in Cambridge, Mass. It was an unconventional childhood but relatively untroubled despite her father’s loss of the hotel and her parents’ divorce.

As a young women Pam White found work as a model and actress. She later obtained college degrees in psychology and social work from Simmons College and Boston University. She became a guidance counselor at Milton Academy, a prestigious boarding school while raising three children.

“She was incredible,” Banker White said. “She was just very supportive of everything that I did, and she also always seemed very interested and connected to what all of us kids did. . . .I think we all felt emotionally supported by my mother.”

That is the Pam White that comes through in on-screen interviews with family members, friends, and from footage in old home movies. The documentary itself sometimes has the warm, spontaneous feel of a home video. But at other times it’s almost almost painfully voyeuristic as the camera brings us in close, and flashes of White’s vivacious, capable self give way to a state in which she struggles with incoherence and anxiety.

Even the setting — a well-to-do New England home, where almost everything seems in place — is unsettling from the perspective of Pam White, whose world is deteriorating from within.

At times, Banker White and his co-director, Anna Fitch, who is now his wife, strive too hard for stylistic effects that intrude on story, but they also show admirable restraint against the temptation to sentimentalize.

For the most part, the directors, employing Super 8 home video footage and an eavesdropping, almost claustrophobic point of view, allow the viewer unrestrained access to Pam White’s daily ordeal as she struggles against confusion and memory loss, unable at times to comprehend the simplest things about the world around her. The attentive and loving care she receives from her husband of 40 years, Ed White, becomes all the more poignant when the movie captures an unguarded moment of frustration as Pam refuses to go on an outing in their small boat.

In one particularly painful scene, a doctor evaluates the disease’s progression through a simple cognitive test that uses flash cards with line drawings of familiar objects. As the doctor flips through the images, she cannot identify the drawing of a bench.

In one such scene, Pam White struggles to put on a winter coat as if she were toddler who has no idea how sleeves work.

“I found that shot really amazing because I never really understood what she was going through,” Banker White said.

His mother searches for the words to express why she does not want an in-home attendant to help care for her. After a struggle, she finds the word she’s looking for: “pride.”

Since wrapping the movie last year, Banker White says his mother’s disease has progressed dramatically, robbing her of more speech, her depth perception, her ability to use silverware or climb the stairs.

“One of the things that I miss most with my mom is my being able to call her and check in with any significant milestone that’s happening with my life, in terms of a relationship or a professional something,” Banker White said.

But he said he also still finds the deep emotional connection that illuminates his movie.

“I still feel like I have wonderful interactions with her,” Banker White said. “And you can share emotion and there are still points of recognition. Part of that is her wonderful smile still exists and she seems very emotionally in tune with everyone she’s around.”