NEURODEGENERATIVE GENETIC DISORDER Huntington’s disease leads to psychiatric problems and cognitive decline in those who develop it, and has no cure.
The child of a person affected by it themselves has a 50 per cent chance of inheriting Huntington’s, but there is now news for those who may be at risk of the disorder and who want to ensure they receive treatment as soon as possible.
Around 500 people in the Republic of Ireland have the condition, making approximately 2500 people at risk of developing HD, the Huntingon’s Disease Association of Ireland says.
Scientists have identified a set of tests that could help identify whether and how Huntington’s disease (HD) is progressing in groups of people who are not yet showing symptoms.
The latest findings from the TRACK-HD study, published in The Lancet Neurology, could be used to assess whether potential new treatments are slowing the disease – up to 10 years before the development of noticeable symptoms.
Lead author Sarah Tabrizi from University College London’s Institute of Neurology explained that currently, the effectiveness of a new drug is decided by its ability to treat symptoms.
These new tests could be used in future preventative drug trials in individuals who are gene positive for HD but are not yet showing overt motor symptoms. These people have the most to gain by initiating treatment early to delay the start of these overt symptoms and give them a high quality of life for a longer period of time.
HD is caused by the mutation of a single gene on chromosome 4, which causes a part of the DNA (known as a CAG motif) to repeat many more times than it is supposed to. The length of the CAG repeat is known to be a major determinant of the age at which HD symptoms are likely to begin, although its contribution to progression is unclear.
In people without noticeable symptoms, there has been little evidence of a decline in function over two years, limiting the ability to test new drugs early in the disease course.
But in this latest study, the TRACK-HD investigators aimed to identify some of the earliest biological changes in individuals with presymptomatic HD. This would give additional power to predict how the disease may progress beyond that already expected from age and CAG length.
Their research showed that over three years, baseline measures derived from brain imaging were the clearest markers of disease progression and future diagnosis, above and beyond the effect of age and CAG count, in gene carriers up to 20 years before they were expected to show symptoms.
In individuals up to 10 years away from developing symptoms, there was also significant deterioration in performance on a number of motor (movement) and cognitive (intellectual function) tasks compared with controls, and the frequency of apathy increased.
According to Tabrizi, a new generation of drugs will be ready for human trials in the very near future.
Diagnosis in HD is something of an artificial construct at onset of motor symptoms, and this study now gives us a number of other, more well-defined parameters that correlate with disease progression. Something that suggests we’re moving towards a more biological, as opposed to physical, definition of disease progression that reduces the importance of an ‘onset event’ is great news.
She added that by extending the clinical trials to include individuals who are currently free of overt symptoms “there is a realistic future possibility that treatments in the pipeline can significantly improve the quality of life for patients and families”.
For more information or support, visit the Huntington’s Disease Association of Ireland website.