A groundbreaking study published in Nature has revealed that subtle yet significant changes in brain structure and protein biomarkers can be detected long before the clinical diagnosis of certain neurodegenerative diseases in carriers of pathogenic repeat expansions. By leveraging whole-genome sequencing (WGS) data and integrating it with extensive neuroimaging and biochemical datasets from the UK Biobank, researchers have mapped the pre-symptomatic effects of expansions in genes such as HTT, CACNA1A, and C9orf72. This pioneering work sheds light on early disease mechanisms and offers promising avenues for preemptive diagnosis and intervention in devastating neurological disorders.
The study delved into the complex relationship between repeat-length polymorphisms in specific loci and brain atrophy patterns typically associated with Huntington’s disease (HD), spinocerebellar ataxia (SCA), and motor neuron disease (MND). The team analyzed MRI-derived volumetric phenotypes from over 66,000 participants alongside plasma levels of nearly 3,000 proteins, including neurofilament light (NfL), a hallmark biomarker of neurodegeneration. Their methodology employed robust linear modeling to correlate pathogenic repeat lengths with both regional brain volume reductions and protein expression profiles, revealing a nuanced portrait of preclinical neurodegeneration.
Intriguingly, expansions in the HTT gene, known for causing HD, demonstrated a pronounced negative impact on the volumes of the putamen and caudate nuclei—subcortical structures critical to motor control and cognitive functions. Among undiagnosed carriers, even those harboring premutation-range repeats exhibited over 4% volume loss in these regions compared to normal-range carriers. Pathogenic carriers showed a staggering 20% or more decrease, pinpointing microstructural brain degeneration well ahead of onset. These findings corroborate and extend previous observations of brain volume loss in familial HD, underscoring how prodromal changes can be detected at population scale.
Similar phenomenon were reported for repeat expansions in CACNA1A, implicated in hereditary ataxias, where cerebellar grey matter demonstrated a dramatic 24.6% volume reduction in pathogenic carriers without clinical diagnosis. This cerebellar atrophy aligns with the known regional vulnerability in SCAs, emphasizing that volumetric MRI phenotypes can serve as sensitive proxies for early neurodegenerative pathology. Moreover, carriers of pathogenic expansions in C9orf72, a locus associated with amyotrophic lateral sclerosis and frontotemporal dementia, showed substantial thinning of the thalamic region by approximately 9%, again revealing that structural decay precedes symptomatic disease.
These significant volumetric changes were meticulously adjusted for confounding variables and observed in individuals who remained clinically undiagnosed over an average follow-up period exceeding four years post-imaging. This temporal dimension of the study design rules out reverse causality where clinical disease might influence imaging outcomes, solidifying the evidence for early pathological changes. Notably, the majority of pathogenic repeat carriers had no documented clinical progression to overt neurodegenerative syndromes, highlighting an important prodromal phase amenable to surveillance.
Complementary to imaging data, proteomic analyses illuminated distinct molecular signatures tied to repeat length expansions. Most noteworthy was the 1.9-fold increase in plasma neurofilament light chain (NfL) levels seen in carriers of pathogenic HTT expansions. Elevated NfL, a sensitive marker released upon axonal injury, aligns with neurodegeneration and mirrors brain volume loss, providing a non-invasive biomarker to track early disease. Although changes in NfL associated with C9orf72 expansions were less pronounced and only significant when comparing pathogenic carriers to normal, these data collectively underscore the systemic molecular perturbations accompanying genetic vulnerability.
Interestingly, expansions in CACNA1A did not demonstrate significant correlations with peripheral NfL concentrations, suggesting locus-specific differences in biomarker expression or pathogenic cascades. This heterogeneity challenges assumptions of uniform biomarker dynamics and demands locus-tailored approaches for monitoring preclinical neurodegeneration. The convergence of imaging and proteomics presented in this study thus offers a multidimensional understanding of how genetic repeat expansions manifest across biological scales prior to clinical disease.
This investigation stands out for its use of deeply phenotyped population cohorts, made possible by the UK Biobank’s unique linkage of genomic, imaging, and proteomic data in tens of thousands of individuals. Such scale and resolution allow discovery of subtle pre-diagnostic signals, hitherto inaccessible in smaller familial or clinical samples. By excluding individuals with diagnosed disease from analyses, the research highlights genuine pre-symptomatic biological alterations and opens doors for predictive modeling of disease risk at the population level.
Importantly, the evidence for localized brain atrophy that parallels classical disease pathology provides a foundation for rethinking intervention timelines. If neurodegenerative processes can be detected years in advance, there is a critical window for therapeutic strategies aimed at halting or delaying progression. Early detection via combined imaging-genetic screening and plasma biomarkers could revolutionize management, shifting paradigms toward prevention rather than reaction.
Moreover, the findings urge reconsideration of genetic screening policies and counseling, as many carriers of pathogenic expansions remain undiagnosed and asymptomatic for extended periods. Enhanced understanding of genotype-phenotype correlations in pre-symptomatic individuals can refine prognoses and inform recruitment into clinical trials targeting early disease stages. This is particularly urgent for disorders like HD, SCA, and MND, where disease-modifying treatments are actively sought and early trial enrollment is paramount.
The investigative team also demonstrated that whole-exome sequencing (WES) data, while not as precise as WGS for repeat-length estimation, corroborated trends seen in WGS for HTT and CACNA1A, suggesting that existing genomic datasets could be harnessed for broader screening efforts. However, accuracy and resolution remain critical for clinical application, emphasizing ongoing technological advances in sequencing.
Overall, this study marks a seminal advance in the understanding of how pathogenic repeat expansions exert preclinical neuroanatomical and molecular effects detectable in the general population. Through comprehensive integration of genetic, neuroimaging, and plasma proteomic data, the authors have elucidated early signatures of neurodegenerative diseases that could transform diagnostics, prognostics, and therapeutic strategies across a spectrum of devastating conditions.
As repeat expansions gain recognition as pivotal contributors to neurodegeneration, these population-scale insights fuel optimism that future interventions might arrest disease processes long before irreversible damage occurs. The synergy of genomics with cutting-edge imaging and biomarker analysis invites a new era for neuroscience—one focused on early detection, preventive medicine, and individualized care pathways.
Subject of Research: Genetic repeat expansions and their preclinical effects on brain structure and protein biomarkers in neurodegenerative diseases.
Article Title: Population-scale repeat expansions elucidate disease risk and brain atrophy.
Article References:
Pounraja, V.K., Sul, J.H., Herman, J. et al. Population-scale repeat expansions elucidate disease risk and brain atrophy. Nature (2026). https://doi.org/10.1038/s41586-026-10345-6
