MOVIE REVIEW : A Bracing Prescription : ‘Lorenzo’s Oil’ takes an unsentimental look at a boy’s devastating disease . . . and his parents’ struggle to cope.

Where most movies lie, “Lorenzo’s Oil” tells the truth and pays the price. In a genre rife with romantic sentimentality, this film won’t trifle with its integrity and ends up not artificially uplifting but heart-rending and exhausting. Based on a true story, it shows how dreadfully hard you have to fight to make a difference, and how grueling it can be to save even a single human life.

That life belongs to Lorenzo Odone, a bright little boy of 5 frolicking in the Comoro Islands (where his father Augusto works for the World Bank) when the film opens in 1983. Soon the Italian-born Augusto (Nick Nolte) and his linguist wife Michaela (Susan Sarandon) return to Washington and what to all appearances will be a satisfying and idyllic life.

Suddenly, three months after the family’s return, Lorenzo starts having inexplicable tantrums and fits of baffling, erratic behavior. He undergoes the usual batteries of tests before the awful news is passed on to his parents: Lorenzo has adrenoleukodystrophy, ALD for short, a rare disease whose effects are as devastating as they are irreversible.

Identified only 10 years earlier and affecting only small boys, ALD destroys the fatty sheath (called myelin) that surrounds and protects the body’s nerves. Once the myelin is gone, the degeneration of the brain and the nervous system is both relentless and inevitable: almost without exception, those afflicted die within three years of diagnosis. Because ALD is an orphan disease, too small to attract major funding, there is no hope of a treatment, not even a hint of a cure, nothing to be done but go home and watch your son die a slow and terrible death.

The Odones think otherwise. They decide to treat Lorenzo’s illness like a foreign country they are about to move to, learning the language of science, studying the literature, teaching themselves everything there was to learn until they know as much about ALD as the doctors. They open a colloquy with Professor Gus Nikolais (a hard but fair Peter Ustinov), the reigning expert on the disease, they expose Lorenzo to a variety of harsh experimental treatments, and, most of all, they search tirelessly for a way to stop his body from destroying itself.

Though in rough outline, “Lorenzo’s Oil” (selected theaters, rated PG-13) sounds uncomfortably like the pro forma Disease of the Month movies that appear on TV with sodden regularity, its thrust and intentions couldn’t be more opposite, as the participation of director (and co-writer with Nick Enright) George Miller makes clear.

With a resume that includes all-out action classics like “Mad Max” and “The Road Warrior” as well as the cacophonous “The Witches of Eastwick,” Australian Miller is the last person you’d expect to be involved with a project like this. But Miller was a doctor before he was a director, and he has always been interested in stories that are strong enough (as “Lorenzo’s Oil” definitely is) to handle his particular brand of narrative intensity.

Working with accomplished cinematographer John Seale (who shot seven features for Peter Weir, including “Picnic at Hanging Rock” and “Witness”) and a trio of editors, Miller has focused on getting this particular story told as energetically and urgently as possible without loading it down with superfluous sentiment. The pace is brisk, the visuals strong, and the acting focused, as everything in the film is, on the refreshing idea that this true-life adventure is as exciting and unnerving in its own way as any ambush Mad Max ever wandered into.

And though young Lorenzo (played initially by Zack O’Malley Greenburg and then by five other boys as his age and medical condition change) is inevitably portrayed as a model little boy, the film that bears his name has been careful not to idealize either the struggle that goes on around him or the people who engage in it.

This careful dispassion covers Miller’s decision to show the ravages of the disease in measured but wrenching and relentless bursts of pain as well as the evenhanded way he deals with the two major forces who lock horns with the Odones as they begin to make progress toward an unconventional treatment, the authority-conscious parents of other ALD kids and the doctors and researchers who wield that authority.

For while the Odones want to save their son, scientists like Ustinov’s Dr. Nick and the parents who are in thrall to them have a different set of priorities and a different timetable. For clinically usable results, trials have to last months, and months are what the Odones, ever conscious of Lorenzo’s deterioration, feel they do not have.

“Lorenzo’s Oil” is also notable in the way it doesn’t flinch from showing the affects this unending battle has on the Odones themselves, most especially on Michaela. Profoundly shocked by the knowledge that she is the carrier of the defective gene that causes ALD, Michaela throws herself into the search for a cure and the care of her son with a steely determination that is more Lady Macbeth than Mother Teresa.

Adopting an icy hauteur that is both protective and a weapon, Michaela battles with and alienates just about everyone she comes into contact with, even husband Augusto (an effective performance by Nolte despite a continually bothersome Italian accent). Far from being the conventional saintly parent, Michaela (played with exceptional force by Sarandon) shows us how a tragedy like this can twist a personality and reminds us that a mother’s love can be an almost frightening thing.

Because “Lorenzo’s Oil” tries so hard to be faithful to the Odones’ experience, it does not elicit the conventional feel-good response these kinds of movies habitually offer. Rather, echoing the Swahili warrior saying that opens the film, it celebrates the struggle, offering us a harsh dose of honesty and reality. The truth can be difficult to take but finally it is the only thing that matters, and the only thing that lasts.

‘Lorenzo’s Oil’

Nick Nolte: Augusto Odone

Susan Sarandon: Michaela Odone

Zack O’Malley Greenburg/: Lorenzo

Peter Ustinov: Professor Nikolais

Kathleen Wilhoite: Deirdre Murphy

Gerry Bamman: Dr. Judalon

Margo Martindale: Wendy Gimble

A Kennedy Miller production, released by Universal Pictures. Director George Miller. Producers Doug Mitchell, George Miller. Executive producer Arnold Burk. Screenplay George Miller & Nick Enright. Cinematographer John Seale. Editor Richard Francis-Bruce, Marcus D’Arcy, Lee Smith. Costumes Colleen Atwood. Production design Kristi Zea. Art director Dennis Bradford. Set decorator Karen A. O’Hara. Running time: 2 hours, 20 minutes.

MPAA-rated PG-13 (child’s life-threatening ordeal).