As many as one in 400 people have the mutated gene that causes Huntington’s disease, Scottish and international researchers have discovered.

The number is far higher than previously thought but suggests many people with Huntingdon's in their DNA do not go on to develop the full-blown condition, scientists said.

Symptoms of the disease - which causes involuntary movements and psychiatric problems - usually only develop later in life. They steadily worsen and lead to death within 20 years.

Researches at at Aberdeen University, the University of British Columbia in Canada and America's Coriell Institute for Medical Research measured the gene for the inherited condition, which is called HTT, and published their findings in this month's Neurology, the medical journal of the American Academy of Neurology.

Their work is the first to reveal how common the genetic cause of Huntington’s disease is in the general population.

HTT contains a section where three letters of the DNA code are repeated. Most people have up to 27 repeats in the gene. People with more than 40 repeats develop the disease, as do some of those with 37 to 39 repeats, although the latter tend to be older.

Until now it has remained unclear how many people in the general population have the additional repeat mutation that causes Huntington’s disease, and how many of them are at risk of developing it.

Professor Zosia Miedzybrodzka, a co-author on the study at the University of Aberdeen, said: "As more and more people are tested for genetic conditions, it is increasingly important for healthcare workers to accurately explain what such gene variations do and don’t mean. We don’t want people who will never get the condition having a gene test for another reason being worried about it in error or disadvantaged in some way. On the other hand, recognising the disease in more people who actually have problems from it should improve their medical care."

The study was funded by the Canadian Institutes of Health Research with the assistance of the Coriell Institute for Medical Research and the NHS Grampian Huntington’s disease endowments research fund.