For 22 years, I had been waiting for a miracle  -  that my brother Lorenzo would be cured. Doctors had warned my father and stepmother that Lorenzo would not see his eighth birthday: boys with his condition rarely survived two years after their diagnosis. But Lorenzo had overcome so many setbacks that it really did seem possible that he would recover.

Last week, when, one day after his 30th birthday on May 29, Lorenzo died, I was in shock.

My whole adult life had been coloured by his presence, on a bed with a suction machine to stop him choking on his saliva, his parents and a nurse nearby in the living room of the family home.

Lorenzo Odone in later years

It was Lorenzo's story that taught me about hope, love and duty. But my brother's story also taught me about the loneliness of the visionary, the selfishness of our culture, and the arrogance that blinds many scientists.

Three years after my parents divorced, when I was 13, my father remarried Michaela, an American publisher. She was soon pregnant and Lorenzo was born on May 29, 1978.

He grew into a remarkable boy, a funny and articulate child who spoke English, Italian and French and favoured opera over nursery rhymes.

I can remember sitting on the stairs outside our house telling him the story of Sleeping Beauty for the umpteenth time. 'No, Ninna,' he would chide me, 'you forgot to hiss when you were the wicked fairy.'

But in 1984, when Lorenzo turned six, tragedy struck. As Michaela sat reading to him one day, he asked her why she was speaking softly. 'Stop whispering, Mommy,' he pleaded, 'I can't hear you.'

Michaela was worried: Lorenzo's kindergarten teachers had been concerned about his short attention span and clumsiness. She decided to have his hearing tested.

The test results were inconclusive, but the consultant, having studied Lorenzo closely, feared there was a deeper neurological problem.

What began as a routine check swiftly ushered in a dark period of blood tests, brain scans and magnetic resonance imaging scans.

The final verdict was unforgiving: Lorenzo had adreno-leukodystrophy, ALD, a rare genetic disorder carried by the mother and affecting boys aged between four and eight. Within a very short space of time Lorenzo would be unable to hear, move, see  -  even swallow. The next stage would be death.

Fighting spirit: Lorenzo as a boy

My father and Michaela were devastated. I remember my father's voice breaking over the telephone (the family home is in Virginia and I was working as a journalist in London), as he said: 'The doctors told us to go home and pray: there's nothing to do.'

But here is where Lorenzo's story departs from the ordinary. Neither my father nor my stepmother had had any scientific training. Yet they decided to research their son's disease.

They took turns, with my father taking unpaid leave from his job at the World Bank, to look up medical annals and scientific reviews in the National Institute of Health library, a few minutes' drive from their home.

They understood that adrenoleukodystrophy was creating fatty acids that Lorenzo's system could not break down. These acids were accumulating in the nerve cells, eroding the white coating, or myelin, that wraps nerve endings and allows the smooth transmission of messages to and from the brain.

In this way, Lorenzo's brain could not send a signal to move his arm or swallow a piece of bread.

My father and stepmother worked against the clock, watching their son deteriorate daily, hoping to find a cure.

Lorenzo's Oil

Miraculously they did. Or rather, they found Lorenzo's Oil, a mixture of oleic and erucic acids, compounds that can be extracted from olive and rapeseed oils and which can stop the production of the damaging fatty acids.

Erucic acid was regarded in America as highly toxic, and U.S. companies were reluctant to make the medicine. But Michaela discovered a company in Hull, Croda Universal, that was ready to manufacture the combination of oils to my father's specifications.

The experiment worked. The oil stopped ALD in its tracks. Tragically, it could not restore Lorenzo's sight, his impaired hearing, or his ability to walk or swallow. It was a therapy, rather than a cure. The little boy remained bedridden  -  trapped, as his mother put it, in a body ravaged by disease.

But there was hope: my father was convinced that if scientists could accelerate their research into diseases such as Lorenzo's, they would find a way to restore him to his old self.

Moreover, both parents proudly pointed to Lorenzo's fighting spirit that threw off every sniffle that had doctors shaking their heads woefully.

The tale of two parents who, motivated by love of their son, discovered a therapy that had eluded the medical establishment was soon taken up by the media.

In America, my father and stepmother were interviewed on TV and made the cover of People magazine; in his native Italy, my father became a national hero. To this day, I cannot show my credit card to an Italian shopkeeper without being besieged with questions about Lorenzo and praise for my father's heroic struggle.

Phil Collins wrote a song, Lorenzo, to lyrics by my stepmother. Even Hollywood came calling: George Miller, the director who went on to make Happy Feet, convinced my father and stepmother that Lorenzo's story deserved a global audience, to inspire other parents with children in similar conditions.

During the making of the film, Lorenzo's Oil, Nick Nolte shadowed my father from home to office. In particular, he told us, he wanted to capture my father's Italian accent.

The result had my father huffing crossly that Nolte made him sound like an ice cream vendor in New York's Little Italy. Meanwhile, Susan Sarandon, herself a devoted mother, punctiliously studied Michaela, becoming her friend in the process.

Friends: Michaela Odone with Susan Sarandon

The film came out in 1992. My father and Michaela were satisfied with the accuracy of its portrayal. Doctors begged to differ. Studies conducted with Lorenzo's Oil were inconclusive, they claimed, and the Odones were peddling false hopes. Most refused to prescribe the oil to their patients with ALD or other similar diseases, like MS.

Undaunted, my father and Michaela founded a charity, the Myelin Project, to promote their vision of medical research: it should be conducted not by scientists locked up in labs competing with one another for a breakthrough, but by scientists in collaboration with one another  -  and with the families of the afflicted.

This was revolutionary: at annual conferences held by the Myelin Project, researchers would meet parents whose sense of urgency was greater than any hope of a Nobel prize.

The men and women used to sealing themselves off among microscopes and glass vials were brought face to face with Anne, the mum of a seven-year-old with ALD, or Joe, a 25-year-old with MS.

Scientific progress is about PEOPLE

The point was brought home forcefully: scientific progress is not just about academic laurels, but about real people.

Some researchers jumped at the chance to engage with people whose lives were affected by disease; but many criticised the venture as wrong-headed. How could mere lay people keep up with scientists' discussions? Why should scientists put up with an extra level of accountability?

If my father and stepmother's attitude to medical research was unusual, their decision to keep Lorenzo at home was treated with even more suspicion.

Friends of the family, former colleagues of my father's, even relatives urged them to farm out Lorenzo to a specialist home, where he could be kept out of sight. I remember the horror on a friend's face when he learned that Lorenzo was at home.

He, who had loved the film and applauded the theory behind the Myelin Project, could not cope with the mess and self- sacrifice that illness entailed.

He was shocked when I explained that my stepmother only rarely left her son's bedside, and that my parents had given up going to the theatre, cinema and parties in order to dedicate themselves to their son. 'What kind of quality of life did they have?' he asked, uncomprehending.

I tried to explain that Michaela and my father could do no differently. Their beloved son needed them. The fact that Lorenzo was unable to fend for himself made this a moral, as well as an emotional, imperative.

My father and Michaela saw themselves not only as the loving parents of an ALD child, but as human beings with an immense respect for, and duty to, life.

In a culture where grandma is put in a home if she becomes incontinent and a disabled child is seen as a burden, this goes against the grain.

What of Lorenzo's own quality of life? Did his gentle, wide-eyed expression belie suffering, or did he bask in the love that surrounded him? It was difficult to gauge, as Lorenzo could rarely communicate  -  by turning his head or blinking.

But as doctors had given him only two years to live and he survived 22 more, I believe that he did want to live. This was a tribute to his parents' extraordinary care.

In order to make Lorenzo feel at the centre of the household, Michaela moved his bed into the living room. There she would read to him or play him music, while nurses worked in shifts to dress, bathe and feed him.

So that he could be assured the best round-the-clock care, Oumouri Hassane, a friend from the Comoro Islands in the Indian Ocean, where the family spent three happy years, was brought over to help nurse him.

Oumouri, now married and with three daughters, has been with us ever since.

Don't tune him out

Michaela, my father and Oumouri insisted that everyone talk to Lorenzo.

No one should try to tune out the boy lying immobile on his bed. Lorenzo's expression sometimes registered pleasure, as when his mother sang to him or Oumouri massaged his legs and feet. It sometimes also registered pain, when a seizure would have him coughing and spluttering.

When his mother died of lung cancer, in 2000, Lorenzo was aware of her absence and his wail echoed through the house.

Michaela's death robbed her of an important victory. In 2005, research published in the Archives of Neurology fully vindicated Lorenzo's Oil. A ten-year study conducted by the late Dr Hugo Moser, the world authority on ALD, showed there was a statistically lower incidence of developing ALD's symptoms in boys yet to show signs of the disease who followed a diet with the Oil.

It had taken 13 years, but finally the medical profession gave its support to the therapy.

I last saw Lorenzo two months ago. I was with my husband and daughter Isabella, four, and I thrilled at the way she spoke unselfconsciously to Lorenzo, describing her school day and favourite toys. With a child's unerring recognition of vulnerability, she held his hand tenderly, almost protectively.

My brother looked well, and as usual my father, Oumouri and I spoke of the 'what if' that haunted our lives. What if Lorenzo outlived our father? Would Oumouri and his family move into the house to continue giving Lorenzo home-care? Would Lorenzo survive a flight across the Atlantic?

In the end, Lorenzo saw to it that we stopped worrying. When my father rang to tell me that he had passed away I wept, partly in sorrow, partly in relief. I wondered what my father would do now that his great mission had ended.

Before I could ask him, he explained he was going to write a book about Lorenzo, for all the schoolchildren who through the years had sent him cards and letters. My little brother had inspired a medical breakthrough, a movie and a song, so why not a book?

'Why not?' indeed. Those two words seem a fitting motto for my father  -  and Lorenzo.