D008 Exploring plasma and CSF small RNAs as early biomarkers for Huntington's disease

<h3>Background</h3> Clinical diagnosis of Huntington’s disease (HD) relies on motor symptoms, but premanifest carriers show brain imaging and cognitive changes decades earlier. In this context, identifying early biomarkers is crucial. Extracellular small RNAs (sRNAs) are promising biomarkers due to their sensitivity to pathobiological processes. Easily found in biofluids as freely circulating or encapsulated in extracellular vesicles (EVs), sRNAs offer a minimally invasive biomarker source. <h3>Aims</h3> To define sRNA-based biomarkers for monitoring pre-symptomatic HD changes by exploring plasma and cerebrospinal fluid (CSF) sRNA levels. <h3>Methods</h3> EVs were isolated from plasma via size-exclusion chromatography and ultrafiltration. EV-sRNA content was profiled using sRNA sequencing, and differentially expressed candidates were validated by qRT-PCR and conducted longitudinal analyses. The same candidates were examined in the CSF. We also evaluated their diagnostic potential and correlations between sRNA expression and clinical assessments. <h3>Results</h3> Most sRNAs in plasma HD-EVs were downregulated compared to Control-EVs, with changes evident at premanifest stages associated with cognitive performance. Seven candidates (tRF-Glu-CTC, tRF-Gly-GCC, miR-451a, miR-21-5p, miR-26a-5p, miR-27a-3p, and let7a-5p) were validated by qRT-PCR showing significant diagnostic accuracy at premanifest stage. Of these, miR-21-5p was significantly decreased over time; and miR-21-5p and miR-26a-5p levels correlated with cognitive changes in the premanifest group, suggesting these sRNAs as novel progression biomarkers. Specific plasma-validated sRNAs were significantly altered in the opposite direction in CSF samples from the same patients. <h3>Conclusions</h3> Plasma and CSF sRNAs are early deregulated in HD, reflecting disease progression and cognitive changes. These findings define a novel early RNA-based biosignature for HD, enhancing early diagnosis and patient management.