Huntingtons disease (HD) is a devastating inherited neurodegenerative condition that causes a slow but relentless decline in mental health, thinking processes, speech, swallowing and balance, resulting in uncontrollable jerky movements.

Those who have the condition will eventually lose the ability to walk, talk, eat, drink, make decisions or care for themselves. A fatal condition, it typically takes between 15 and 25 years from a person developing symptoms until they die. These symptoms generally begin between the ages of 30 and 60 but can appear before or after this range.

The disease is caused by the faulty Huntingtin gene that expresses a toxic protein, (also called Huntingtin) which builds up and causes early brain-cell death. The child of someone with Huntingtons has a one in two chance of inheriting it, so people at risk grow up experiencing the impact on family members as they become aware of their own likelihood of getting the disease.

Although worldwide research is taking place, there is currently no cure for Huntingtons disease. However, the effects of many of its symptoms can be reduced with a combination of medication, dietary advice and non-medical therapies, including physiotherapy and speech therapy as well as appropriate social care and support.

Nearly 40 years ago, 9.94 per 100,000 people in the north of Scotland had symptoms of Huntingtons, compared to 5.4 per 100,000 elsewhere in the UK. Now our latest research has revealed that 14.6 people per 100,000 in this northernmost region have Huntingtons. The current figure for rest of the UK is 12.4 per 100,000, illustrating that rates are rising generally, but remain particularly high in Scotland.

Our research team decided to re-run a 1984 study that had examined the prevalence of Huntingtons in the Grampian region. We used medical records from labs and HD clinics across the Highlands and Grampian regions to count the number of people across the north of Scotland tested and diagnosed with the condition in the intervening years. Remarkably, we found that cases have increased by 46% since 1984.

In addition, over the last four years, 23% more people with no symptoms but a personal or family history of HD have had a genetic test to see if they will develop the condition possibly in the hope of taking part in trials that might slow the disease.

Our findings mean that northern Scotland has among the highest rates of Huntingtons disease in the world. Its prevalence is almost three times greater than reported elsewhere in Europe (4.7 per 100,000); North America (4.1-5.2 per 100,000); Japan (0.1 per 100,000); Australia (5.70 per 100,000 people) and more than five times the estimated worldwide rate of 2.71 per 100,000 people.

Since the identification of the Huntingtons gene in 1993 made testing for the condition possible, awareness has increased and a diagnosis can now be made in people unaware of their family history of the condition. Along with better care and hope of treatment trials, this has led to more people coming forward for testing.

We believe the high rates of HD diagnosis in Grampian and Highland are due to a combination of underlying genetic susceptibility in ancestral populations dating back to the rule of the Picts; increased awareness that diagnosis will lead to better care and support services; and the region having one of the oldest specialist Huntingtons research clinics in the world. Interestingly, there is also a higher incidence of of multiple sclerosis (MS) in the north of Scotland, though no equivalent genetic explanation for some of the cases.

We did note that the rates of Huntingtons also vary between the different health board regions in the north of Scotland, with more cases in Highland and fewer in Orkney and Shetland compared with Grampian. This local variation in rates could have major drug cost and service delivery implications for the NHS, especially if expensive, complexly administered therapies prove successful.

Although the condition is particularly common in northern Scotland, our data clearly shows that there is far more Huntingtons diagnosed now than the previous prevalence studies suggest, and more people with the HD gene are testing before the appearance of symptoms to access better care and research trials.

The increased diagnosis rate for Huntingtons is likely to be even greater in regions around the world where there has been no long-term focus on the diagnosis and management of the disease.

Health care providers worldwide should now assess local need for specialist services in the expectation that Huntingtons is more common than previously thought. They also need to plan for therapies that can help with the condition, making them part of routine clinical care by improving local services, providing Huntingtons clinics, and studying the prevalence of the disease in their country.

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Huntingtons disease: northern Scotland has one of world's highest rates and rising sharply here's why - The Conversation UK