Scientists believe they may have found a way of slowing the progression of Huntington's disease.

Huntington's is caused by a single faulty gene, and causes gradual and invariably fatal decline.

There is currently no effective treatment or cure for the condition which people inherit from their parents.

It is important to find out what causes nerve cells to be sick and ultimately to die

Dr Oliver Quarrell, Huntington's Disease Association

However, scientists in the US believe they have identified this fault and are hopeful that the discovery could lead to a new treatment for patients.

Huntington's disease is caused by a genetic mutation which inserts a repeated DNA sequence into the gene encoding the Huntington protein.

It is believed that this damages cells by interfering with their energy-producing mechanism or mitochondria.

Cell mechanism

Dr Tim Greenamyre and colleagues at Emory University in Atlanta, Georgia, isolated this mechanism from patients with the disease and from mice which were engineered to have the condition.

They found that they could reproduce the abnormalities associated with Huntington's disease by applying proteins containing the mutation to the mitochondria of healthy subjects.

This has led them to conclude that the direct interaction between the mutant Huntington protein and the mitochondria causes the disease.

Writing in the journal Nature Neuroscience, the authors said further studies were now needed to find out how exactly the two interacted.

Dr Oliver Quarrell, of the Huntington's Disease Association, welcomed the study.

He said: "We are pleased with any research findings that strengthen our knowledge and understanding of Huntington's disease.

"It is important to find out what causes nerve cells to be sick and ultimately to die. We need that if we are to have any form of effective treatment."

But he added that further research is needed. "This paper makes a contribution but it may not be the key step."

Huntington's happens when cells start to die in a single, small area of the brain which helps control the movement of the body's muscles.

Although the disease is inevitable from conception onwards, symptoms normally appear between the ages of 30 and 50.

Parents who carry it have a 50% chance of passing it on to their children. A blood test can confirm whether or not the mutated gene is present.