It is a rare neurological disorder which affects girls across the globe and can deprive sufferers of their ability to walk.

Rett Syndrome is easy to miss in the first months of life, as babies appear to grow and develop normally.

However, its symptoms become devastating, with epilepsy, muscle weakness and scoliosis - or spinal twisting - among the conditions experienced by patients in later years.

Now a scientist in Scotland’s capital is celebrating after being named joint winner of the world’s most prestigious neuroscience accolade for his groundbreaking work on the disease.

Sir Adrian Bird, Buchanan Professor of Genetics at the University of Edinburgh, said he felt “truly honoured” to be awarded the Lundbeck Foundation Brain Prize alongside Professor Huda Zoghbi.

The pair’s contribution to modern understanding of Rett Syndrome, which affects around one in 12,000 girls born each year, has been massive.

In 1992, Sir Adrian discovered the MECP2 gene, with Ms Zoghbi, who is professor of genetics at Baylor College of Medicine and Texas Children’s Hospital, proving it to be the cause of the disorder.

“I have been fortunate to work with outstanding people over the years, and this recognition from the Lundbeck Foundation is also a credit to them,” he said.

“Like so many discoveries that have turned out to be bio-medically important, the work we began in the 1990s started out as blue-skies research with no obvious practical benefit.

“I am grateful for all the generous support I’ve received from the University, the Wellcome Trust and the Rett Syndrome Research Trust since those early days.”

First described by Austrian doctor Andreas Rett in 1966, the syndrome is caused by a mutation of the MECP2 gene and develops in stages throughout an individual’s life.

During the first months, there is little sign that anything is wrong, although children are often described as “easy and quiet”.

However, at the age of one to two, problems usually emerge.

Youngsters begin to show signs of autism and make repetitive, jerky hand movements.

Low muscle tone and difficulties when feeding can also be observed.

The condition eventually stabilises but the child will remain developmentally disabled.

As well as trouble with breathing or sleeping, patients may suffer from epilepsy and scoliosis, with around half unable to walk.

Male foetuses with the MECP2 mutation typically perish during pregnancy.

In the rare cases when boys do survive, they are usually more seriously affected than girls.

Professor Richard Morris, chair of the Brain Prize’s Selection Committee, said the decision to award the honour to Sir Adrian and Ms Zoghbi, who will also share 10 million Danish krone (£1.17m), was in recognition of “their fundamental and pioneering work” on Rett Syndrome.

“Their work established the importance of epigenetic regulation in both brain development and the maintenance of normal adult brain function,” he added.

“It also points to novel opportunities for treatment of this and other neurodevelopmental disorders.”

Jan Egebjerg, Director of Research at the Lundbeck Foundation, which is celebrating ten years of the Brain Prize, said: “The brain is incredibly complex and, therefore, a great many of its basic mechanisms – for instance, when it comes to disease – are still uncharted territory.

“Brain disorders are a huge burden – to the individual and society alike.

“So, it’s vital that we give a boost to brain research. “Above all, this means giving research more money.

“But it’s also important that we honour the researchers who often dedicate their entire careers to uncovering new territory and to delivering the greatest advances in brain research.

“These are some of the aims of The Brain Prize.”