More people than previously thought have the mutated gene that causes Huntington’s disease, scientists have said, although for many the odds of actually getting it are lower than estimated before.
According to university researchers as many as one in 400 people have the potential to develop the condition – this is ten times higher than estimated before.
A study published in the medical journal of the American Academy of Neurology said the conclusion was drawn from findings in Canada, the USA and Scotland.
Huntington’s disease is an inherited condition, which causes involuntary movements, loss of intellectual abilities, behavioural and emotional problems and leads to death after 15-20 years. It affects 12 in every 100,000 people in the UK.
It is caused by the gene HTT, which contains a section where three letters of the DNA code are repeated. Most people have up to 27 repeats, but people with more than 40 repeats develop the disease, as do some with between 37 to 39 repeats.
Chris Kay from the University of British Columbia in Canada, lead author on the manuscript, revealed the majority of their study subjects fell into the latter category. If these people do develop Huntington’s, it usually starts over the age of 60.
They studied the genes of a total of 7,315 people. Of those, 18 people had 36 or more repeats, which extrapolates to about 1 in 400 people in the general population. Three of those people had 40 or more repeats of the gene.
The study found that people with 36 to 38 repeats had a lower than previously thought chance of developing symptoms of the disease – as low as 0.2 per cent for those over the age of 65 and with 37 repeats.
Study author Michael R. Hayden, a professor at the University of British Columbia, said: “It’s unclear why some people with reduced penetrance genes develop the symptoms of Huntington’s as early as midlife, while others reach old age with no symptoms. Additional genetic and environmental factors may modify the likelihood that a person develops the disease.
“But the high frequency of these mutations in the general public shows that we may be underestimating the number of elderly patients with Huntington’s disease.”
Professor Zosia Miedzybrodzka, a co-author on the study at the University of Aberdeen, said: “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.”
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