Films about the effects of Alzheimer’s—on both those afflicted with the disease and the people who love them—are still rather rare, but those that do exist, like “Away from Her,” “Iris” and “Still Alice,” have maintained a high level of accomplishment. To their number can now be added Elizabeth Chomko’s “What They Had,” a highly personal work based on the writer-director’s own family history that incisively and touchingly sketches the impact a mother’s slide into dementia has on her devoted husband and their grown children.

The woman is Ruth (Blythe Danner), who spent thirty years working in nursing homes—an experience that has made her husband Burt (Robert Forster) deeply suspicious of such places. Now, while she has moments of lucidity, she is more likely not to recognize family and friends. Nonetheless Burt insists on keeping her at home, even after she wanders off into a snowy Chicago night. Their son Nick (Michael Shannon), a bar owner who lives in the area and is always called on to assist when such episodes occur, has had enough. He calls his sister Bridget (Hilary Swank) in California, suggesting that she return to Illinois and persuade their father that it’s time that Ruth be placed in a residential facility where she can be properly cared for.

Bridget has problems of her own. Her marriage to Eddie (Josh Lucas) is on the rocks even if he doesn’t know it, and she arrives in town with her daughter Emma (Taissa Farmiga), an unhappy girl who wants to drop out of college. While in Chicago, in fact, Bridget will flirt with Gerry (William Smillie), an old high school classmate whom she doesn’t even tell she’s still married. That does not go well.

Nor does she fall in with Nick’s plans, which involve persuading their father to sign the papers that will move Ruth into a well-regarded home, with a nearby apartment for Burt. That causes friction with Nick, who’s quick to point out her habit of going along with everything their father decides (which, apparently, included her marriage to Eddie). Nick’s frustrated because he gets no respect from Burt, who dismisses him as a mere bartender and has signed over power of attorney to Bridget instead. But he’s the one who gets called on whenever Ruth gets into trouble.

In the end Chomko ties together the various strands of this dysfunctional family dynamic, resolving the fractures in a poignant way that might strain credibility to some extent but is nonetheless dramatically effective. And throughout she leavens what obviously could have been a very downbeat tale with moments of mordant humor. Shannon and Forster are particularly good at taking advantage of the opportunities they afford. By contrast Swank—who effectively becomes the focal point of the plot—is more serious, and her intensity can get a bit wearying; the same might be said of Farmiga. Both, however, fulfill the script’s demands.

Finally there’s Danner, whose Ruth serves more as a catalyst for the other characters than the focal point of the narrative. Nonetheless she brings to the woman an ethereal presence that makes her scattered moments and mental agitation quite moving.

“What They Had” was shot in the Chicago area, where Chomko grew up, and captures the texture of the city and its suburbs well, with Roberto Schaefer’s unfussy camerawork and the efforts of production designer Chris Stull and costumer Anne Dawson studiously avoiding any inclination to romanticize the material by minimizing the grittiness or prettifying the background. With crisp editing from Tom McArdle, for the most part the film tells its story economically, although the periodic introduction of montages of “home movie” footage and stills showing the happier days of Burt and Ruth’s courtship and marriage can come across as a mite heavy-handed.

Alzheimer’s is a difficult subject to deal with dramatically, and it’s remarkable that the filmmakers who have tackled it thus far have succeeded in treating its ramifications without sliding into disease-of-the-week-style mawkishness. “What They Had” can be added to the small but growing number of good pictures on the subject.