Despite his parents' treatment, Lorenzo did not get better
Lorenzo Odone, whose parents' battle to save him from a rare nerve disorder was depicted in the 1992 film Lorenzo's Oil, has died from pneumonia aged 30.
Doctors had predicted he would not live beyond childhood when he was diagnosed with the incurable disease aged six.
But his parents found what seemed to be a cure made of acids from olive and rapeseed oils.
Lorenzo died at his home in the US state of Virginia on Friday - a day after his 30th birthday.
He was suffering from aspiration pneumonia, which was caused by food getting stuck in his lungs.
His father Augusto said: "He could not see or communicate, but he was still with us. He did not suffer... That's the important thing."
Lorenzo had Adrenoleukodystrophy (ALD), a genetic disease that progressively destroys the brains of young boys.
The disease leads to the build up of dangerous fatty acids - long-chain fatty acids - in the blood, and within a year children are paralysed, blind, and unable to speak. It is invariably fatal.
Lorenzo was given less than two years to live but his parents refused to accept the doctors' prognosis.
With no scientific training, they took on the medical establishment and set about finding a cure.
In 1986 it seemed they had succeeded with a combination of oils that effectively reduced the long-chain fatty acids in the blood.
Despite the fairytale ending in the film, the claims have always been controversial and children suffering from ALD continued to die, despite being treated with Lorenzo's oil.
However, a 10-year study showed that while the oil does not appear to work for people who are already ill, it does seem to prevent illness in those whose genes make them vulnerable to developing symptoms.
Augusto Odone said his son's ashes would be taken to New York and placed with those of his wife Michaela, who died in 2000.
He added that he was planning to move back to his native Italy and write a book about his son.
Actors Susan Sarandon and Nick Nolte played Augusto and Michaela in the 1992 film. Lorenzo was played by Zack O'Malley Greenburg.