The earliest brain changes due to Huntington’s disease can be detected 24 years before clinical symptoms show, a study suggests.

Researchers said their findings could help with clinical trials by identifying the ideal time to start treating the disease.

Huntington’s is a hereditary neurodegenerative disease, and there is currently no cure for it.

Researchers would ultimately like to treat people before the genetic mutation has caused any functional impairment.

These findings provide vital new insights informing the best time to initiate treatments in the future

However, until now it was unknown when the first signs of damage start to appear.

But as there is a genetic test for Huntington’s susceptibility, researchers have a unique opportunity to study the disease before symptoms appear.

Study lead Professor Sarah Tabrizi, of University College London’s (UCL) Huntington’s Disease Centre, UCL Queen Square Institute of Neurology, said: “Ultimately our goal is to deliver the right drug at the right time to effectively treat this disease – ideally we would like to delay or prevent neurodegeneration while function is still intact, giving gene carriers many more years of life without impairment.

“As the field makes great strides with the drug development, these findings provide vital new insights informing the best time to initiate treatments in the future, and represent a significant advance in our understanding of early Huntington’s.”

The Wellcome-funded study, led by UCL researchers in collaboration with colleagues from the University of Cambridge and University of Iowa, investigated a large cohort of Huntington’s mutation carriers at a much younger age than previously looked at in detail.

Sixty-four people with the mutation took part alongside 67 others without the mutation who served as control subjects for comparison.

The study, published in The Lancet Neurology, found mutation carriers were, on average, 24 years ahead of the predicted disease onset, based on their age and a genetic test.

We have found what could be the earliest Huntington’s-related changes, in a measure which could be used to monitor and gauge effectiveness of future treatments in gene carriers without symptoms

They showed no changes in thinking, behaviour or involuntary movements commonly found in the disease, and there was very little evidence of brain scan changes.

But researchers did detect a subtle increase in the spinal fluid of a neuronal protein called neurofilament light (NfL), which is often the product of nerve cell damage.

Just under half (47%) of the mutation carriers had NfL values in their spinal fluid above the range of values found in the control group, at 24 years before disease onset.

The scientists said this suggests they have identified a crucial point at which brain changes first start occurring.

Co-first author of the study Dr Paul Zeun said: “We have found what could be the earliest Huntington’s-related changes, in a measure which could be used to monitor and gauge effectiveness of future treatments in gene carriers without symptoms.”