Results from a "ground-breaking" drug trial have offered new hope to people with Huntington's disease.
The experimental drug, injected into spinal fluid, was shown to lower levels of the harmful protein responsible for the devastating inherited brain disorder.
IONIS-HTTRx is the first pharmaceutical agent designed to target the root cause of Huntington's.
A total of 46 patients with early-stage Huntington's disease took part in the trial, conducted at nine centres in the UK, Germany and Canada.
The study confirmed that the treatment worked as hoped, and was well-tolerated by the participants.
Lead researcher Professor Sarah Tabrizi, head of University College London's Huntington's Disease Centre, said: "The results of this trial are of ground-breaking importance for Huntington's disease patients and families.
"For the first time a drug has lowered the level of the toxic disease-causing protein in the nervous system, and the drug was safe and well-tolerated.
"The key now is to move quickly to a larger trial to test whether (the drug) slows disease progression."
Huntington's disease is a progressive neurological disorder that normally appears in adulthood and causes involuntary movements, psychiatric symptoms, and dementia.
Currently incurable, the condition affects an estimated 10,000 people in the UK. A further 25,000 are thought to be at risk. Patients usually die within 20 years after the onset of symptoms.
The new drug, developed by Ionis Pharmaceuticals, contains an "antisense" molecule consisting of a single strand of chemically-modified DNA.
The DNA strand stops the genetic instructions for making the Huntington's protein getting through to manufacturing machinery in brain cells.
Levels of the toxic HTT protein are reduced, thereby minimising damage to the brain.
Full details of the trial are due to be presented at scientific meetings and published in a peer-reviewed journal next year.
Trial patient Peter Allen, 51, from Essex, told the BBC: "You end up in almost a vegetative state, it's a horrible end.
"It's so difficult to have that degenerative thing in you. You know the last day was better than the next one's going to be."
His mother Stephanie, uncle Keith and grandmother Olive, have all died from Huntington's disease.
Tests show his sister Sandy and brother Frank will develop the condition.
Dr Philippa Brice, from the genomics research charity PHG Foundation, said: "This is a potential game-changer, not only for Huntington's disease patients but also for genomic medicine in general.
"Though more work needs to be done, if gene silencing lives up to this promise we could be on the brink of some of the personalised treatments that patients with severe genetic diseases need so badly. But this will also raise further questions for society and for policy-makers about how best to use such a powerful technique."