Sole survivor: 'It's amazing that he's alive'

A sk Patricia Fitzpatrick the age of her son, Lucas, and she'll be very precise: three years and seven months. "We're proud of the months," she admits. It is little wonder; at one stage, she and her husband were told that their only child, who had been seriously ill, had a fatal illness. Every month that passes is cause for celebration.

Lucas is only the second person in the world to have been diagnosed with the enzyme deficiency 3-hydroxyisobutyryl-CoA hydrolase (HIBCH). At one stage, the protein he ate was poisoning him. He suffered a couple of toxic attacks that damaged his brain, and it was uncertain whether he would survive. It took years for specialists to discover what was wrong with him.

Since his diagnosis, which led to treatment, he has made considerable progress. "He hasn't gone back to hospital for about two-and-a-half years, so when people ask how old he is, we say, 'Three years and seven months.' The seven months really matter for us," says Patricia, 36, who gave up her marketing career when Lucas came ill.

Lucas was born a lively, healthy baby. When he was five months, Patricia and her husband Martin, 37, who owns a heavy plant company, noticed that his head had started to wobble. A GP and health visitor assured them it was nothing to worry about. When, at six months, Lucas still hadn't improved, he was referred to a neurologist at the Royal Free Hospital, who also said there wasn't cause for concern.

Then, at seven months, he started to have "absences" – episodes when he would look up to the sky and blank out for about five seconds. " We didn't think it was too serious, just something that needed treating like a muscle weakness," Patricia remembers. "So we kept going back. It took a good four months to convince someone that something was going on."

That someone was a private paediatric neurologist, to whom the couple had turned in desperation. "She said we needed to go back to the Royal Free Hospital, as it could lead to terrible things and even death. That was when our world fell apart. We entered a nightmare." At that stage, all the expert would tell them was that Lucas had ataxia – a problem with movement and co-ordination.

After returning to the Royal Free, Lucas, then 10 months old, was immediately referred to Great Ormond Street Hospital, where investigations were carried out. But there was no diagnosis.

Several months later, the boy started vomiting after every feed, and his breathing became unusual. He was rushed to hospital. Patricia and Martin were told he was suffering from metabolic acidosis, whereby the body becomes toxic as a result of too much acid in the blood. "We didn't know then, but later found out, that the reason was because when you have too much protein in your body that you can't metabolise well, you become toxic," Patricia says.

Once Lucas was stable, he was taken by ambulance to St Mary's Hospital. "We were told they were not sure whether he was going to make it or not. You feel as though you've died yourself. He was taken to the critical care unit and had gone to sleep. We didn't know if he was going to wake up," Patricia says.

Several days later, Lucas was well enough to be transferred to Great Ormond Street. "When he woke up, we realised that the child who had come back to us was not the same. He went from being a very happy, normal child who was curious and very communicative, who could walk by holding on to the furniture and babble, to being completely disconnected from this world after the episode of acidosis." He had uncontrollable eye movement, as well as dystonia, which meant that his muscles made involuntary movements. " This was not our child." Lucas stayed for a month while tests were carried out. "We didn't fall apart because we couldn't – we needed to help Lucas and understand what was going on. It was a living nightmare."

The boy was seen by numerous doctors, one of whom was Peter Clayton, professor of metabolic medicine and hepatology. When the family left the hospital, Lucas was given a loose diagnosis of a degenerative illness called Leigh syndrome. Sufferers endure episodes of acidosis, regressing until death.

"Normally, children who get it as early as Lucas die in early infancy," Patricia says. "It was a big blow because there was no hope, no treatment. There was nothing you could do except wait for death to come. Professor Clayton had said that it wasn't Leigh syndrome, but that we should go with it for the moment."

Lucas, who was no longer in a critical condition, was discharged. "We were now left with a child who had a million problems with vision, dystonia and bowel problems. Suddenly he couldn't swallow and had to have a tube that went into his stomach to feed him."

Then, in December 2005, Lucas suffered a second episode of acidosis. " It wasn't as bad as the first," Patricia says, "but he still suffered a lot of damage. He became completely out of it, as if he was in his own world. He lost complete movement of his arms and stopped swallowing again."

In the meantime, as well as pursuing investigations with Clayton, the couple contacted experts around the world, sending them blood and muscle samples taken at Great Ormond Street. "We were emailing and constantly faxing, pushing and bothering just to see if somebody else had a different opinion. A lot of them came up with nothing or normal results. Others said that if Leigh syndrome was what Great Ormond Street said, then that's what it was. Others said that if we were dealing with Professor Clayton we were in the best hands possible."

They were right. In March 2006, Patricia and Martin met Clayton again. " He looked really happy and said he thought he knew what Lucas had. He described the case of the only known person who had the same illness, who died in the 1980s – a baby of Egyptian cousins, who died at three months." Two months later, biochemical tests confirmed the condition.

"We used sophisticated analytical instruments capable of detecting a whole range of different chemicals in the blood or urine," Clayton explains. "Lucas had an accumulation of a particular compound in his blood, and I had to ask myself, 'If this is the compound that is accumulating, what is the enzyme that is missing?' Having come up with a candidate for the missing enzyme, we decided to measure its activity in cells grown from a skin biopsy. In collaboration with a laboratory in Amsterdam, we were able to show that this enzyme was indeed defective.

"Then we were able to look at the gene and show that that was faulty as well. It took about six months. It's pretty gratifying when you've had to work it out from first principles. We were very pleased."

And with a different diagnosis came treatment. Lucas is now on a low-protein diet, which consists of one blended meal a day, as well as a low-protein drink. He's given drugs to help eliminate the toxic compounds that accumulate as a result of his enzyme deficiency, as well as vitamins and supplements to replace those he would have got from a normal diet. The improvements have brought considerable joy to his parents. Lucas can now sit, with a degree of support, use his arms and move around with the help of a walker.

"He's happier now and goes to nursery and music therapy. It's nice to see our child back," says Patricia, who will consider IVF to screen out the faulty gene if she and her husband decide to have another child. " He's started vocalising again and we're hoping it will turn into a babble and hopefully he'll utter words. But he's still very unbalanced, which makes it hard for him to crawl.

"We see small improvements all the time, but they are really, really slow. We had hoped that putting him immediately on the treatment would bring back these different skills. But because he suffered two bouts of acidosis, a lot of damage was done to his brain, in particular the area that controls balance and co-ordination."

So what's the prognosis for Lucas? "It looks as though we can prevent the episodes of acidosis, so I hope he will have no further loss of function, " Clayton says. "Being at an age when the brain can recover, he will continue to show positive developmental progress. I hope that Lucas will soon sit unsupported and that he will eventually stand or walk with support. I think that he will acquire language, though it might be difficult to understand. But it is very difficult to be exactly sure what the future holds."

Undoubtedly, Lucas's future is much brighter. "It now feels that we've got a chance," Patricia says. "The fact that he's alive – which wasn't a possibility two years ago – is really amazing."

HIBCH: How proteins can kill

* Lucas has a metabolic disorder. When protein is eaten, it is broken down in the gut into its constituent amino acids, one of which is valine. People can only use a certain amount of valine in the diet to make new protein, particularly when growing. The excess is normally eliminated in the form of urea and carbon dioxide. Lucas, however, has two faulty genes (one from each of his parents) and as a result he can't make one of the enzymes needed to break down valine.

* There have been only two diagnosed cases of HIBCH. There may well be more children with the condition who have been misdiagnosed.

* Acidosis is a life-threatening build-up of acid in the blood, which is caused by a block in a metabolic pathway.

* Acidosis is a life-threatening build-up of acid in the blood, which is caused by a block in a metabolic pathway.

* Two nurses from Great Ormond Street Hospital plan to row across the Atlantic to raise £250,000 for research into metabolic disorders. Herdip Sidhu and Elin Haf Davies will launch on 2 December. Call 020-7239 3000 or email community@gosh.org to donate.