Dina and Scott are very much in love and planning to get married. There’s plenty to do before the wedding, and for many couples this is a daunting time. Dina and Scott have an additional complication, which makes the documentary “Dina” so compelling — in varying degrees, both are on the autism spectrum.

Movies with similar subjects seem to tempt directors to take one of two unacceptable paths: The works can turn out precious or exploitative. Not “Dina.” That’s in part because Dina Buno is a vital and honest character, and she clearly trusts the moviemakers (Co-director Daniel Sickles is an old family friend of hers.).

At age 48, Dina has Asperger’s and some other issues, including OCD and depression. She is articulate but can get flustered at obstacles and has some problems with things like simple addition. She lives frugally on a supplemental income in suburban Philadelphia and, though bright in her own way, spends a fair amount of time watching junk TV.

She’s been married and widowed and has lived on her own for decades, with visits from her mom, with whom she has a somewhat contentious relationship. Several times we catch a view of her bare back, which is scarred.

Scott Levin, who seems a few years younger, is a security guard at Walmart and able to help her with arithmetic, but has his own autism issues (not as clearly spelled out as Dina’s). He loves singing and listening to music and still lives with his parents. He’s a decent, gentle fellow, who loves telling Dina how much he loves her.

He means it, but is he ready for marriage? It’s a big step when he leaves the house where he grew up to move into Dina’s apartment prior to the wedding. Dina can, for the most part, take care of herself, but she’s lonely, and she really wants this to work out.

Sex is a persistent theme in the movie, and it’s handled forthrightly. In short: Dina is experienced and craves touching, while Scott, whose declarations of love are plainly sincere, has issues with any but the most fleeting sort of physical contact.

Dina is aware of the problem; and during their trip to the beach, she hands Scott a present: a copy of “The Joy of Sex,” accompanied by a few questions about his sexual habits and experiences, if any. The subject makes him nervous, though he acknowledges that it’s something he has to work on. It might be an uphill battle, judging by how much time he spends with his nose buried in his cell phone.

Undoubtedly the most intense scene happens late in the film, an abrupt and unexpected departure in tone that immerses us in the most traumatic moment of Dina’s life, played out against the image of an empty bench seen against a darkening evening sky. It’s a risky moment, and the filmmakers (Sickles and Antonio Santini) pull it off exceptionally well.

“Dina” — which won the U.S. Documentary Grand Jury Prize at Sundance this year — declines to offer an uplifting resolution. As the film details Dina’s past, the mood becomes more serious, and it’s by no means obvious that the newlyweds will overcome their substantial problems. But although there may be no fairy-tale endings, by the movie’s end it’s impossible not to wish one for Dina and Scott.

MOVIE REVIEW

“Dina”

Grade: B

Starring Dina Buno and Scott Levin. Directed by Antonio Santini and Daniel Sickles.

Unrated. Check listings for theaters. 1 hour, 42 minutes.

Bottom line: Compelling documentary about couple with autism