The number of people who have the gene that causes Huntington’s disease in Northern Scotland has been accurately counted for the first time in 35 years in new research from the University of Aberdeen.
The research used NHS family-based records to find that there are more than 160 adults living in the area who have the Huntington’s gene but have not been tested.
However, the scientists behind the study believe the figure will be even higher as not everyone with Huntington’s disease symptoms seek diagnosis.
The study, published in Neuroepidemiology, confirmed that Northern Scotland has one of the highest rates of Huntington’s disease in the world at 14.5 per 100,000 people, it is more than five times the estimated worldwide rate of 2.71 per 100,000 people.
Huntington’s disease runs in families, and every child of someone affected has a 50:50 chance of inheriting the gene. The gene slowly damages the brain, eventually taking away the person’s ability to walk, talk, eat and drink, make their own decisions and care for themselves.
The new analysis showed that, on average, every person who has been diagnosed with Huntington’s disease will have at least another 2.2 relatives who have the gene. This means there are hundreds of people in Northern Scotland who could be considered for effective treatments for Huntington’s disease when these become available in the future.
The research was led by University of Aberdeen’s Professor Zosia Miedzybrodzka who is also clinical lead for Huntington’s disease in North of Scotland (covering Grampian, Highland, Orkney, Shetland, and the Western Isles), based in NHS Grampian, alongside Heather Cruickshank, Genetic Counsellor in NHS Grampian.
Previous studies have mainly looked at the number of people who tested positive for the Huntington’s disease gene then estimated the number of relatives at risk using statistical modelling. However, in this study, scientists used family tree clinical records to count how many people have a 50:50 chance of having inherited the neurodegenerative condition but, crucially, have not been tested.
This meticulous approach has not been used in the UK since the Huntington’s disease gene was discovered in 1993.
The authors stress how important it is to generate a clear picture of the number of people with Huntington’s disease in the region to ensure that care planning objectives are met and reinforces the need to invest in specialist care and support to help people impacted by what is a notoriously complex and difficult to manage condition.
Professor Zosia Miedzybrodzka
Professor Miedzybrodzka said: “Previous work looked at how many people in the area have been tested for Huntington’s disease, that is people diagnosed with Huntington’s disease signs and those with a gene alteration that will develop the condition in later life. However, no one has properly counted just how many people who haven’t been tested yet must have the gene.
“It is crucial that we know this number, and that it is accurate, so that health boards can properly plan now for care, and for treatments when they become available in the future.
“A 2022 Scottish government report underestimated Huntington’s disease rates and did not account for numbers of people at risk in a way that our clinic and lab data has.”
Heather Cruickshank added: “In 1989, when scientists previously studied this, testing was not possible, fewer people had a diagnosis of Huntington’s disease, and families were larger.
“But even now, despite high rates of testing, most people at risk of developing Huntington’s disease in Scotland have not had a test.
“There is a massive worldwide effort seeking treatments for Huntington’s disease.
“Going forward, services need to plan to treat these as yet uncounted people, as well as those currently diagnosed. Regional variations in rates will become more important, including genetic counselling and testing, management, and treatment delivery. Furthermore, better knowledge of the numbers of people who could benefit will encourage investment into drug discovery.
“Having a test remains a free choice for people from Huntington’s disease families and our research means that care can be planned for all those at risk, without people who don’t want a test having one.”
Commenting on the findings of the study chief executive officer of Scottish Huntington’s Association, Alistair Haw, said: “Earlier this term a Scottish Parliament motion calling for an expansion of specialist Huntington’s disease services in light of rising cases became the most supported motion in the history of devolution. This latest study further strengthens the case for immediate action to expand specialist services for families impacted by Huntington’s.
“Huntington’s disease is a hugely complex, widely misunderstood and extremely difficult to manage condition. Specialist services are not some 'nice to have' optional extra but an absolute necessity to prevent patients reaching crisis point and presenting to acute emergency statutory services. Specialist Huntington’s services need to be expanded urgently – a message further reinforced by this new and clear evidence which has major implications for health and social care providers throughout Scotland and beyond.”