Huntington’s is an inherited condition that is caused by a defect in a particular gene. This is responsible for making a protein which does not work properly in people with the disease.

Over many years, this “mutant” protein forms clumps in brain cells and causes them to become damaged and die.

At the moment, no treatments exist that can alter the course of Huntington’s disease but some medicines help with symptoms.

In the new clinical trial, patients are being given a drug called ALN-HTT02 to see whether it can reduce levels of the protein that causes damage to the body.

A man who does not wish to be named became the first person treated in the global trial a few weeks ago, receiving the therapy at University College London Hospitals NHS Foundation Trust (UCLH).

Up to 54 people are now being recruited to the trial and will receive either a single injection of ALN-HTT02 or a dummy drug.

Anyone given the placebo will be given the option of whether or not to receive ALN-HTT02 in the future.

Professor Sarah Tabrizi, director of the Huntington’s Disease Centre in London and a consultant at UCLH, said: “We are very excited about this trial as the drug, ALNHTT02, targets a specific region of the HTT gene called exon 1, which we now think is a key toxicity driver of the damage seen in Huntington’s disease.

“Our end goal is to explore the potential of this medicine to slow disease progression and, in this first-in-human study, we are evaluating the safest ways to use ALN-HTT02.

“I am so pleased we have begun this important and innovative trial, which we hope will bring us closer to an effective treatment for Huntington’s disease and make a meaningful difference for patients and families affected by this devastating condition.”

There are thought to be around 7,000 people living with Huntington’s disease in the UK, which is passed down via a parent.

If a parent carries the faulty gene, there is a 50% chance of each of their children developing the condition.

Symptoms of the disease include memory problems, depression, difficulty moving and problems swallowing, speaking and breathing. It is usually fatal 10 to 30 years after symptoms develop.

The sponsor of the new trial is Alnylam Pharmaceuticals, which has co-developed the drug with Regeneron Pharmaceuticals.

ALN-HTT02 is a type of molecule called a small interfering RNA (siRNA).

It is designed to lower production of the protein from the faulty gene.

During the trial, the drug will be administered through an injection into the fluid around the spinal cord.

Kevin Sloan, a vice president at Alnylam said: “We’re thrilled to be collaborating with established leaders in the space to advance an investigational RNAi therapeutic that we believe has the potential to alter the course of this devastating disease.”

The journalist and global spokesman for patients and families with Huntington’s, Charles Sabine, said: “When I was tested and found to have the Huntington’s disease gene, I was told there was nothing I could do about the disease, which had already taken my father, my uncle and my older brother.

“Since then, I have shown there is everything I can do.

“I have participated in observational trials to develop the biomarkers that are needed to measure new treatments - by taking blood we have been able to ascertain a new successful marker for neurodegeneration, called neurofilament light.

“I have also participated in clinical drug trials themselves.

“These trials cannot work without human involvement - patients volunteering - and I’m so proud of everyone who does.

“The science is now at a point that new therapies are being tested and giving us real hope for the future.”