Research brief
Huntington’s disease (HD), an inherited neurodegenerative condition, is traditionally diagnosed after the onset of motor symptoms. However, a recent study from researchers at University College London, published in Nature Medicine, reveals that neurodegenerative changes begin decades before clinical symptoms appear. The study presents somatic CAG repeat expansion in blood as a predictor of early brain changes, offering a potential new biomarker and therapeutic target for delaying disease progression.
The Mechanisms of Somatic Expansion
An expanded CAG repeat in the HTT gene causes Huntington’s disease. The length of this repeat strongly influences the age at which symptoms begin. Researchers found that these repeats undergo somatic expansion throughout life, with longer repeats causing faster neurodegeneration. The study demonstrates that somatic expansion, even in blood, reflects changes occurring in the brain, making it a valuable proxy for monitoring disease progression.
Dr. Sarah Tabrizi, lead author, explains, “This study provides the first in vivo evidence that somatic CAG repeat expansion drives early neurodegenerative changes in Huntington’s, long before clinical diagnosis. Targeting this process could transform how we treat this devastating disease.”
Early Biomarkers of Neurodegeneration
The researchers studied individuals who carried the HD mutation but were decades away from expected symptom onset. They found that even in these early stages, biomarkers in cerebrospinal fluid (CSF) revealed significant changes:
• Neurofilament Light (NfL): A marker of neuronal damage, levels of NfL in CSF increased rapidly in individuals with the HD mutation.
• Proenkephalin (PENK): A surrogate marker of striatal medium spiny neurons, PENK levels were reduced, indicating early striatal damage.
• Brain Atrophy: Imaging studies revealed that the caudate and putamen, brain regions affected by HD, showed accelerated volume loss.
Implications for Treatment
The findings highlight the potential of targeting somatic expansion as a therapeutic strategy. Drugs that modulate DNA repair pathways—such as those involving the mismatch repair protein MSH3—could slow or prevent this process, delaying the onset of clinical symptoms. These insights also suggest that somatic expansion in blood could serve as a non-invasive biomarker for monitoring the efficacy of such therapies.
What’s more, the study underscores the importance of early intervention. By identifying and treating individuals in the preclinical stages, brain function may be preserved, and the onset of symptoms delayed, offering hope for improved outcomes in Huntington’s disease.
A Step Forward in Huntington’s Research
This study not only enhances our understanding of Huntington’s disease but also provides a roadmap for developing preventative treatments. By focusing on somatic expansion and its role in early neurodegeneration, researchers are uncovering promising avenues to combat this debilitating condition.
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