Archie Strachan was two when he displayed symptoms of the disease that has since blighted his life. “One night he started screaming in pain,” said his mother, Julia. “Doctors flew Archie to hospital, where we eventually found he was suffering from a condition called pulmonary arterial hypertension.”

The disease, known as PAH, leaves the sufferer breathless, exhausted and prone to heart failure. Twenty years ago it was considered a death sentence; even today the condition – which affects around 6,500 people in the UK – is considered debilitating and life-limiting.

However, thanks to the team of doctors and scientists involved in treating Archie, it is hoped that a drug which could block the disease’s progress could be developed in a few years. Writing in Nature Medicine last week, the group –led by Professor Nick Morrell of Cambridge University and funded by the British Heart Foundation – reveal that they have pinpointed a protein that circulates in the bloodstream and plays a crucial role in ensuring our lungs’ blood vessels are healthy.

“We have discovered that patients suffering from pulmonary arterial hypertension don’t make enough of this protein, which is known as BMP9,” Morrell told the Observer. “We have carried out tests that indicate that the protein, which is relatively easy to manufacture, could restore blood vessels in patients’ lungs to a healthy condition.”

Pulmonary arterial hypertension is caused by a narrowing of the blood vessels that lead from the heart to the lungs. When these arteries narrow, it becomes harder and harder for the heart to pump blood through to a person’s lungs. This disrupted blood flow leads to major health problems. Current treatments only target the symptoms and the prognosis remains poor; the only long-term treatment is a lung transplant or a heart-and-lung transplant.

“The trouble is there is a very limited supply of donated heart and lung combinations, particularly for children, and the survival rate for those who get transplants is about 50% after five years,” added Morrell.

The nightmare facing PAH patients, particularly those who develop the disease in their early years, is demonstrated by the story of Archie, who lives in the Cotswolds with his parents, Jamie and Julia. After his diagnosis, his condition deteriorated rapidly and he had to be treated with 24-hour intravenous medicine to alleviate his symptoms. “He was fitted with a device that could continually administer his medicine, which was stored in a little back pack,” said Julia.

However, Archie’s condition worsened and he eventually underwent an operation to allow more blood to get round his body. But the blood now contains much less oxygen, and this could lead to organ failure in later life.

Morrell’s work suggests there is hope that Archie’s prospects could improve. “The protein we have identified – BMP9 – is crucially for keeping the lining of blood vessels in the lung in a healthy condition,” he said. “In proper quantities, it prevents arterial cells from leaking or dying off. Without enough of it, blood vessels in the lungs narrow and become misshapen and blood cannot get through. This forces the heart to work harder and harder – until it fails. Raising levels of BMP9 in patients’ blood should get round that problem.”

In animal tests BMP9 didn’t only prevent pulmonary arteries from becoming narrow, it restored already damaged blood vessels. “We hope that will be the case with humans,” said Morrell. Phase-one safety tests of BMP9 should start within the next year and should lead to phase-two efficacy trials within two or three years, he added. “A key feature of BMP9 is that it is made in the human body and so should not trigger immune reactions. Certainly we are hopeful.”

Professor Jeremy Pearson of the British Heart Foundation added: “These findings offer real promise of a cure. They could be a game-changer.”

Archie’s parents have set up their own charity, the Dinosaur Trust – reflecting Archie’s love of dinosaurs – to raise funds for research. “It is impossible to explain the pain we have gone through since Archie’s diagnosis, but now we have this light at the end of the tunnel, and that is wonderful.”