This does take us closer to some effective treatment

Sue Watkin, chair of the Huntington's Disease Association

Symptoms usually start in middle age.

But American scientists from the Johns Hopkins Medical Institutions, in Baltimore, have discovered how a mutant protein produced by the gene responsible for Huntington's disease triggers the death of nerve cells.

Armed with that knowledge, the researchers have reversed cell death in laboratory cultures of human cells containing the HD gene.

Abnormal gene

Lead researcher Christopher Ross, said: "Obviously, our goal has been to understand HD's mechanism so we can interfere with it earlier on with drugs.

"We've long known that the abnormal gene produces a flawed form of a protein called huntingtin."

The brain cells of patients with HD show characteristic clumping of huntingtin.

And although the molecule itself is not harmful it does attract another protein called CBP.

When the two become entangled it leads to the genetic material of the cell being rendered useless.

The scientists added a bogus version of the CPB protein after snipping out the molecular areas normally attracted to huntingtin's. This enabled it to survive.

Rescue cells

Professor Ross said the change, reported in the journal Science, was remarkable.

"Instead of degenerating, cells in these cultures remained healthy. We were able to rescue them completely."

They have so far not been able to replicate the laboratory experiment in a live mouse, but say proving the principle of the research is an important step to perfecting a cure.

"We haven't yet demonstrated the turnaround in a live mouse model. Our research so far, however, offers a needed target for developing and testing new drugs."

Sue Watkin, chair of the Huntington's Disease Association, said the scientists seemed to have made a real breakthrough in the fight against the disease.

"We are excited by that, but we always have to be a little bit cautious because every time something is portrayed as the breakthrough, but this does take us closer to some effective treatment.

"The fact that this one seems to be very specific to cell survival seems to suggest that it is very significant."