My brother Lorenzo Odone, who has died of pneumonia a day after his 30th birthday, became famous worldwide as the inspiration behind Lorenzo's oil. The oil, a therapy for sufferers of adrenoleukodystrophy (ALD), a debilitating and ultimately fatal condition, was discovered in 1990 by his parents, Michaela and Augusto Odone. Two years later, their extraordinary achievement - neither had any medical training - was turned into the Hollywood movie Lorenzo's Oil, directed by George Miller and starring Susan Sarandon and Nick Nolte.
Lorenzo was born in Washington DC; he was Augusto's third child but his only offspring with Michaela, his second wife. Soon after his third birthday, Lorenzo moved with his family to the Comoro Islands, in the Indian Ocean. Augusto, an economist with the World Bank, had been sent to the archipelago to set up the Comoros Republic's first financial plan. Michaela had given up her job as a publishing editor when her son was born.
His time in the Comoros - an unspoilt tropical paradise once under French colonial rule - was the happiest in Lorenzo's life. A lively and charming boy, he displayed a precocious gift for languages as he mastered English, Italian and French. He was funny, articulate and favoured opera over nursery rhymes.
One anecdote from his early years reveals his spirited approach to life. Shortly after arriving on the islands, he was invited to a party full of French, Belgian and Comorian children. Despite being the newcomer in their midst, he at once tried out his first sentence in French: "I am the leader; follow me."
In 1984, the Odones returned to Washington. But from the outset, Lorenzo seemed unsettled and unhappy in his new surroundings. Michaela worried about teachers' reports that commented on her son's short attention span and moodiness. Then one evening, as she sat reading to him, Lorenzo asked her to speak up. "Mommy, why are you whispering?" he asked.
Alarmed, she immediately took him for a hearing test. The consultant found the hearing normal, but after studying Lorenzo closely, feared a neurological cause for his difficulties. He ordered a battery of tests, which led to a devastating diagnosis: ALD. A rare genetic disorder, carried by the mother and affecting only boys between the ages of four and eight, it robs its victims of their sight, hearing and ability to swallow and walk before finally killing them - typically, within 24 months.
Michaela and Augusto listened as the doctors explained that there was nothing to do but let the disease take its course. Lorenzo's nervous system was under assault from long chain fatty acids. These were accumulating and damaging his myelin, the white matter that coats nerve endings and allows smooth transmission of messages to and from the brain.
The parents listened - and then rebelled. They refused to go home and watch their beloved son slowly die. Instead, despite having only the equivalent of a science A-level between them, they began a round-the-clock rota at the US National Institute of Health Library, a few minutes from their home in the Washington suburb of Chevy Chase. Within a year, after poring over experiments and theories in medical journals, Augusto realised that a combination of erucic and oleic acids would stop the production of the long chain fatty acids in Lorenzo's system. The Odones called the cocktail of acids Lorenzo's oil, and Croda Universal, a British firm in Hull, began its manufacture. Once the oil became part of Lorenzo's diet, his condition stabilised.
The extraordinary tale of two lay people discovering a therapy that had eluded the scientific community quickly spread. Media interest, and a contract with Universal Pictures to turn their life story into a film, allowed the Odones to set up a foundation, the Myelin Project, which is today active in the US, Canada, Britain, Germany and Italy. The aim was to accelerate research into the de-myelinating diseases - such as ALD and the more prevalent multiple sclerosis (MS) - to restore Lorenzo's faculties as quickly as possible.
Michaela and Augusto had managed to arrest the progress of the disease, but Lorenzo was still bed-bound and unable to move, hear, see or swallow. To give a greater sense of urgency, the Myelin Project organised regular international conferences, where scientists met families of those afflicted by de-myelination.
Not all members of the scientific community welcomed this approach; or, indeed, their portrayal on film as hard-hearted and arrogant. A backlash against the Odones saw various researchers from around the world denying the efficacy of Lorenzo's oil, and most doctors refused to prescribe it. In 2005, however, the world's top authority on ALD, the late Dr Hugo Moser, published the findings of a 10-year study which showed that a statistically lower incidence of ALD occurred in those boys whose diet included Lorenzo's oil.
The vindication came too late for Lorenzo's mother, who died of lung cancer in 2000. But Augusto, aided by Oumouri Hassane, a family friend from the Comoros who had become Lorenzo's chief carer, continued to keep his son at home. By now the family had moved to Fairfax, Virginia. In the living room - at the heart of the household - Lorenzo lay on his bed, or was placed on a specially fitted armchair, with a nurse and his father, or Hassane, beside him at all times. He was read to, exercised, and played music to, his every breath and expression constantly monitored.
His determination to live on was daily on display: he overcame every cold, fever and even pneumonia, that had doctors, and his family, fearing for his life. His courageous battle inspired not only Miller to make his movie, but Phil Collins to write a song, Lorenzo, in 1996; and schoolchildren from all over the world to write in their wishes for his recovery.
In the end, though, the odds were too high against survival. He had lived more than 20 years longer than doctors had predicted, and was almost certainly the oldest survivor of ALD in the world.
Lorenzo is survived by his father Augusto, his brother Francesco, myself and his friend Oumouri.
· Lorenzo Michael Murphy Odone, born May 29 1978; died May 30 2008